i did read liked three or two times
Then you have a problem, because it is clearly said how to.
but iam saying do u need a program or nothing
to change a model just rename the one you want into the one you want it to be
Do I need to go into textures?
well he does need a program to get the files from the rez files. but other then that no u dont need a program.
3 programs really
Converter/rexextract/rezinject
For model change, he doesn't need anything. But for getting the model files he need RezExtractor to extract the .rez and RezInject to inject the modded files.