Computer problem, Please help?

Hi, me and my brother want to start playing WoW together because we hate it when its solo. Im on my dads computer and i need to clear 4.4GB of space. Iv cleared over 10GB but theres seriously nothin else i can think of doing. Does defraging clear much space? I did it for about 1hr and only like 15% was done and i cant leave the computer on that long to maybe get a little bit of space. Im really into computers but im scared i might delete 1 of those "DO NOT TOUCH!" programmes like a driver updater(etc). What should i do? Theres only like 70GB on it, its a total rip off, its like 4-5yrs old and cost 1.100€ and it cant even run WoW at "recommended" settings i think. And the thing is, it has wireless internet and we dont know the password and he doesnt want to be in his room to have to play his laptop. Is there anyway to find out the password if we dont know it, and how can i clear up more space. THANKS ALOT DAWGS