right, what you need firstly is Carset Creator, there is one in the downloads section under Editors/Utilities.
then, using it, browse the GPI files that are in the game and find the 2 drivers that you don't want anymore in the folder GP4>Menudata>PC?GP2001>Imgaes
when you have found the 2 drivers you don't want, remember what number their files were.
then get your new GPI files, and simply rename the file (right click, rename) to the number of the old driver.
then put the 'new' gpi files in to the same folder, and overwrite the 'old' drivers.
then check it in game, and it should work.
RIP Jules, never to be forgotten. #KeepFightingMichael