I can't find in the manual how to change the title screen, the first thing you see when you start the game. Do you know how to change that?
Viewing post in The Definitive Guide to the Raycasting Game Maker comments
It's discussed in the section that starts at the bottom of Page 47. I'm not sure if I described it as well as I could, but I believe it all makes sense if you read the entire guide in context. That's my bad for not repeating some things at the beginning of sections.
Basically, the "gamebitmaps" folder will contain the Entering Next Level screen, Finished screen, HelpScreen, Menus 1 2 and 3, Sound screen, and the "IntroScreen." Every file must maintain the exact same file name at all times, otherwise RGM won't see it or recognize it. So as you design your own Menus and the IntroScreen, you need to make a copy of it with the same name as the files you want to replace, then overwrite those files in the "gamebitmaps" folder.
So in your case, you'd want to design an intro or title screen, export a copy of the finished image as "IntroScreen.bmp," then copy/paste that over the file in the gamebitmaps folder. Once you overwrite it, RGM should automatically display it when you start building your game level and testing the level out.
I'm not sure why the smaller "MenuMaker" program doesn't include the Title screen as one of the things you can import and adjust, but it excludes it for some reason. So it has to be swapped out manually.