what
monk_56 wrote.
or if you really want to delete a CG of the game, i'd advise against it, as the event for that CG will still happen, but now the game will throw errors at you.
for whatever reason you want a CG gone, you can however easily replace it with a, let's say, black-screen.
for example you want the CG "abbey gb" gone. you exchange the file "abbey gb.png" with a file of the same name you created in the game files. just go into your folder where you saved the game files and go to the location \game\images\CG .
you probably don't have these folders right from the start, so you first have to unpack them with a tool like Unren, which you can find here on this site. use the unren.bat in your main folder and extract the RPA packages, this should create the subfolders you need.