The answers above will work for changing the values.
If you want to change the number of cells in your list (e.g. I have a list called 'revisions' which has 4 items, I now need 7 items) you will find that you can't simply select your list and amend it on the sheet, So:
go to your 'Formulas' tab
choose "Name Manager"
a pop up box will show what is available for editing. Your list should be in it. Select your list and edit the range.