Why is my laptop so slow?

I recently bought this used laptop and the guy i bought it from claimed he was a computer tech. guy, and said he changed alot of things on the computer such as he put something in it and now it can have alot more memory and he made it so it can play blu-ray movies. But now i am afraid to restart the computer to factory settings because of all the changes he has made, It has windows seven, and is soooo slow, sometimes i will simply click to turn on music and it wont even open the music files. Should I just be brave and restart the computer to factory defaults?