It depends on which section of the application you are hoping to change. After you hit Submit you can only change the following sections:
ID Numbers.
Name, including Full Legal Name, Preferred Name, and Alternate Names.
Contact Information including Permanent and Preferred Mailing Addresses.
Alternate Contact Information.
Date of Birth, Birth Address, and Sex.
Letters of Evaluation (only additions of up to 10 letters and notifying the AMCAS application of a letter no longer being sent).
Your next MCAT testing date.
Add Medical Schools and change existing Program type (deadlines, fees, and restrictions apply).
Choosing to release your application information to your pre-health advisor.