What happens a lot of times is that when you put ram in the motherboard will run it at whatever the default speed is and if you have ram that is supposed to run higher all you have to do is go into the bios and change the frequency to the speed that it is supposed to be. Once you hit enter on the ram frequency all of the available options come up and it's just a matter of selecting the one you want.
Memory: 2x 240pin DDR3-1333(OC)/1066/800 DIMMs, Dual Channel, Non-ECC/Un-buffered, Max Capacity upto 8GB
This is the ram spec's of that board and you will notice that the 1333mhz is overclocked (OC) and the board will support natively 1066 and 800 mhz dual channel up to 8gb.
Here are some ram kits that you could look at and decide if you want to go with 4gb or 8gb and because the MB supports it you can run these at 1333mhz overclocked.