Replacing ROMs

[BigBen19]

I have taken the advice of others who've suggested trying different ROM's to settle on one. However, before I do this, I need some help with changing from one to the next. The phone has been unlocked, but are there certain procedures I need to follow to remove the current ROM (one I've downloaded, not stock) and put a new one on. Or if anyone can point me to a stick/instructions that would be just as good.

Thanks