Pentium G3258 is a good gaming cpu if you overclock it, but your motherboard would'nt allow much of stable overclock. I think I'd change the cpu for something like i5 4690 or 4460.
Tha CPU is not made to run stock ahahah, you have to get a decent cooler and overclock the hell out ot that CPU if you want it to perform
You cannot expect to overclock 'the hell out' of G3258 with a AsRock H81m board. This is why I think he should upgrade to a bigger cpu and run at stock speed (or light overclock).