There isn't really any reason to upgrade that CPU.
sunder25 :
If you want better gaming performance, upgrading the GPU is the way to go.
As for the PSU, as the fellows above mentioned, you are fine.
The whole thing is great for gaming actually. No need to upgrade anything for games. But maybe he wants to do advanced video editing or wants to run lots of virtual machines. If so then a Core i7 would be a good upgrade. But we simply have no more info to determine if the upgrade is worth it.