system slow, with frequent errors
 

Howdy! - my nephew called me in tears. He has Linux and it barely crawls anymore, crashes frequently, and has very little memory left. This in spite of that he uses only a few sites and has not much in the way of programs, music and photos downloaded. The system came used from his school when they upgraded. He's been through a number of Firefox user accounts trying to speed things up and claims to have deleted the old accounts, but says info tied to those acct's still pops up. Any tips on how to approach cleaning up his system would be greatly appreciated! (I'm o.k. with Windows, but I understand it's apples & oranges.)

How full is his hard drive? No operating system likes it when the hard drive begins to get full?
Also what distro is he using. If he's using an old Ubuntu, (which i have a suspicion he is) or any no longer supported version of a distro, then he won't be getting any of the upgrades including any security updates which will leave his computer in a vulnerable state.