Raise your multiplier in the bios, run Intel Burn Test, if you crash you're not stable.
If you don't crash, you need watch your temps with a program like HW Monitor and don't break 60C.
If you break 60C you need a better cooler.
If you still have thermal headroom you can keep upping your multiplier.
If you aren't stable and still have thermal headroom then you can slowly up your voltage until you get to 1.5V