The CPU currently in it is a E-300 or something like that, the new CPU needs to be socket FM1 in order for it to fit into the socket let alone work. Also, the PSU is a mere 220w.
As for the question "what WILL fit the mobo socket?" - the answer is: Nothing that would be worth performance gain. Tell him - don't bother. If he wants a faster/better PC, tell him to sell this one and get a slightly more customization build/PC.
These computers weren't ever designed to be upgraded like that.