this is a difficult question for me to answer in a few words, we modified quite some parts and they were done step by step.
current bbs is vbb 2.8 if i didn't remember wrongly, actually modification of the forum is not difficult, if your friend would like to make his forum more attractive, he can install hacks like what we did, just follow the instruction of the installation, with some basic knowledge of html, php and mysql, it won't be difficult.