Nothing is likely to be easy in your case - you have a Template Monster template, and they are known for disabling standard Zen Cart functions and writing their own code to do only what the designer thinks it should do (and clumsily, too).
Because they change so many things, it can be hard for us to advise based on ZC knowledge. There are known fixes for some of the TM messes.
Do a search for Template Monster to see what is in store.