You can select a chamfer and directly edit a chamfer to change the chamfer value or you can indirectly edit the chamfer to move a face that adjoins a chamfer.
Select a chamfer.
Click the chamfer edit handle.
Type a new value for the chamfer and click.
Click to complete the edit.
Select an adjoining face of a chamfer.
Click the move handle.
Move the cursor until the face is positioned approximately where you want it, then click.
Click to complete the move.