<PAGE>

                                                                    Exhibit 10.4

                                    AMENDMENT

                                       TO

               EMPLOYMENT AGREEMENT DATED AS OF SEPTEMBER 13, 2002

            THIS AMENDMENT ("Amendment") to the Employment Agreement by and
between Legato Systems, Inc., a Delaware corporation (the "Corporation"), and
David L. Beamer (the "Executive"), is made as of this 16th day of September,
2002.

            WHEREAS, the Corporation and the Executive entered into an
Employment Agreement dated as of September 13, 2002 (the "Employment
Agreement");

            WHEREAS, Section 26 of the Employment Agreement provides that the
Employment Agreement may only be amended by a written instrument signed by the
Executive and an authorized officer of the Corporation; and

            WHEREAS, the Corporation and the Executive now wish to amend certain
provisions in the Employment Agreement, in order to provide the Executive with
an additional time period to exercise his option to purchase shares of the
common stock of the Corporation following the involuntary termination of his
employment, among other things.

                     NOW, THEREFORE, in consideration of the mutual promises and
covenants contained in this Amendment and of other good and valuable
consideration, the sufficiency of which is hereby acknowledged, the parties
hereto agree as follows:

            1. The definition of "Involuntary Termination" in Part One of the
Employment Agreement is hereby amended and restated in its entirety to read as
follows:

            Involuntary Termination means (i) the Corporation's termination of
the Executive's employment for any reason other than a Termination for Cause, or
(ii) the Executive's voluntary resignation within one hundred eighty (180) days
following (A) a material reduction in the scope of his duties and
responsibilities or the level of management to which he reports, (B) a reduction
in the aggregate dollar amount of his base salary and Target Bonus by more than
fifteen percent (15%), (C) a relocation of his principal place of employment to
a location that is more than fifty (50) miles from his then primary place of
residence, or (D) a material breach by the Corporation of any of its obligations
under this Agreement and the failure of the Corporation to cure such breach
within sixty (60) days after receipt of written notice from the Executive in
which the actions or omissions constituting such material breach are specified.

            An Involuntary Termination shall not include the termination of
Executive's employment by reason of death or Incapacity.

            2. Part Three, Paragraph 14(e) of the Employment Agreement is hereby
amended and restated in its entirety to read as follows:

            Extension of Exercise Period. For each outstanding Option (i) which
is granted to the Executive on or after September 13, 2002 or (ii) which is
outstanding on that date and is not otherwise listed as an excluded Option on
attached Schedule I, the Executive shall have until the earlier of (i) the
expiration of the twenty-four (24)-month period measured from the date of his
Involuntary Termination or (ii) the expiration date of the option term in which
to exercise that Option. To the extent the exercise period of any existing
Option which is an incentive stock option under the federal income tax laws is
so extended, that Option shall be deemed to be regranted on the date of this
Agreement and may accordingly fail to retain

                                        1

<PAGE>

such incentive stock option status by reason of the One Hundred Thousand Dollar
($100,000) limit on the initial exercisability of incentive stock options per
calendar year or because the exercise price of that Option is below the Fair
Market Value of the Common Stock on September 13, 2002. Accordingly, if the
Option does lose such incentive stock option status, the Executive shall
recognize immediate taxable income upon the subsequent exercise of that Option
in an amount equal to the Fair Market Value of the purchased shares less the
exercise price paid for those shares, and the Executive will have to satisfy all
applicable income and employment withholding taxes at the time of such exercise.
To the extent any such Option does retain its incentive stock option status, the
Executive shall not be entitled to long-term capital gain treatment upon the
subsequent sale of any shares purchased under that Option unless such sale
occurs more than two (2) years after the deemed September 13, 2002 regrant date
of that Option and more than one (1) year after the date such Option is
exercised for those shares.

            3. Schedule I to the Employment Agreement is hereby amended and
restated in its entirety to read as follows:

                            LIST OF EXCLUDED OPTIONS

            The following Options currently held by the Executive shall not be
modified pursuant to Paragraph 14(e) of the Agreement to provide the extended
twenty-four (24)-month exercise period following the date of his Involuntary
Termination. Accordingly, for each of the Options listed below, the Executive
shall continue to have only until the earlier of (i) the expiration of the
option term or (ii) the end of the period specified in the applicable stock
option agreement for which that Option is to remain exercisable following the
date of his termination of employment with the Corporation, including an
Involuntary Termination.

            Grant Date        Number of Option Shares            Exercise Price
            ----------        -----------------------            --------------

            4. Except as expressly set forth herein, all of the terms and
provisions of the Employment Agreement shall remain unmodified and in full force
and effect, and the Employment Agreement shall be read together and construed
with the applicable sections of this Amendment.

            5. This Amendment may be executed in several counterparts, each of
which shall be deemed an original, but all of which together shall constitute
one and the same instrument.

            6. Capitalized terms used but not otherwise defined herein shall
have the meaning ascribed to them in the Employment Agreement.

            7. The provisions of this Amendment shall be construed and
interpreted under the laws of the State of California applicable to agreements
executed and wholly performed within the State of California. If any provision
of this Amendment as applied to any party or to any circumstance should be
adjudged by a court of competent jurisdiction to be void or unenforceable for
any reason, the invalidity of that provision shall in no way affect (to the
maximum extent permissible by law) the application of such provision under
circumstances different from those adjudicated by the court, the application of
any other provision of this Amendment, or the enforceability or invalidity of
this Amendment as a whole. Should any provision of this Amendment become or be
deemed invalid, illegal or unenforceable in any jurisdiction by reason of the
scope, extent or duration of its coverage, then such provision shall be deemed
amended to the extent necessary to conform to applicable law so as to be valid
and enforceable or, if such provision cannot be so amended without materially
altering the intention of the parties, then such provision will be stricken, and
the remainder of this Amendment shall continue in full force and effect

            8. This Amendment, together with the Employment Agreement as amended
hereby, shall supercede and replace any prior agreement between the Corporation
and the Executive relating to the subject matter hereof.

                                        2

<PAGE>

               IN WITNESS WHEREOF, the undersigned have executed this Amendment
as of the day and year written above.

                                     LEGATO SYSTEMS, INC.

                                     By:    /s/ George I. Purnell
                                          ------------------------------

                                     Title:  Vice President, Human Resources &
                                             Chief Learning Officer

                                       /s/ David L. Beamer
                                     -----------------------------------
                                     DAVID L. BEAMER

                                       3