The stock cooler is not made for overclocking and if you want to get good overclocking and lower temps then you should invest in an aftermarket heat sink like the Cooler Master EVO 212. It will only run you about $30 at Amazon.
The other thing that you want to remember is that Prime95 is a stress testing software and will stress the CPU 100% so the temps that you get with Prime will be the top mark for the high temp and with everyday use , even gaming you will not come close to that temp. The 76c is not that high with using a stock cooler but you should get a better cooler if you like to overclock , the lower the CPU temp the better.