Are you using a 64 bit OS?
Your CPU can handle all of the RAM your mobo supports. Your mobo most likely can handle 16GB+. Depending on what version of the O/S you are using will determine if you can use 8GB or more RAM. All 32-bit O/Ss are limited to a total of 4 GB. 64-bit O/Ss can use far more RAM - again depending on which version you are using. Below is an example of the limitations in the 64-bit versions of Win 7 & 8.