Im working with the rpg2 game but i dont understand how to change existing assets, for example the loading logo. Can anyone give me some pointers?

Well, first of all you have to identify it.
One way is going through the code, and in the loading/intro state look for BLUE markers (they indicate UIDs, which are the way in which assets are used in code).

they will display the project name of the particular asset. You can use that to search in the project files for the asset. You can now modify it, or if you want to replace it just replace the BLUE UID in code with the one for your asset (drag the asset and drop it in code will write the UID of the asset in code for you).

I'm not good at explaining, but I hope this made sense. Let me know if there's something unclear.