Alright since everyone complaining about almost everything, here's the new update
BACKUP EVERYTHING IN CASE YOU NEED IT SOMETIME!
All you have to do is extract the rar, repack the DATA and GFXGEM mod folder to your original .mix file
Now unpack your original RiderRacing.mix file
Copy and replace the extracted .mix files with the modded "CHARACTERS" folders
Then repack and replace with your original RiderRacing.mix file