If you only wish to change just one end then push the cursor to that end of the object and press the left button. The object section becomes active such that up and down movement of the mouse causes the object end section diameter to 'grow'. Each of these can be entered by either pressing numerical keys or F5. If after snapping to an object you choose a position on the object other than an end then both ends of the object will become active. See the user manual for further details.
Various commands require numeric input.
Some of these commands automatically activate the 'number menu' so that a number can be selected using the mouse. If the exact value cannot be obtained simply begin pressing numeric keys or press F5 to enter new values. Sheet Lightning is not restricted to working in millimeters or any other units of measurement. ALT-X is the quickest and easiest way to quit the program. Otherwise select 'Quit' in the 'File' menu of the 3D CAD environment or the 'Quit' button in the parametric environment.