How do you mod GTA IV?

I installed GTA IV (NOT TBOGT OR TLAD, JUST THE ORIGINAL ONE) on my flash drive. I have been searching everywhere but I can't find out how to mod GTA IV online or offline with mods like Speed, Cars, God mode, etc. At one point I downloaded a file with mods in from Robatore because he just said GTA IV 5.5 Modz so I downloaded it and saw common.rpf and other stuff. I know you are supposed to replace those with the ones from the game but I don't see anything in my flash drive when I open it in usbxtafgui v44. (A tool for modding) All I see in there is stuff like Data01 Data02 Data03 and stuff. Can someone give me a website or something that tells me how to Mod gta iv offline or online (<