How much and what kind of RAM can my MSi motherboard utilize?

My system's mainboard is a MSI 785GM-E65 and it curently has 2 Gigs of system RAM (2x1 GB Kingston HyperX 1333)

I've been searching what my memory configuration possibilities are for expanding and I cannot figure out what to buy. It is DDR3 memory. Do I have to remove the 2x1 GB and install a fresh pair of ie 2x4 GB? Or can I add 2x4 GB next to this 2x1 GB?

What's best?

PS. the manual was translated from chinese and I cannot make sense of it.

According to the MSI official page found here MSI Global ? Motherboard - 785GM-E65

Your motherboard supports four unbuffered DIMM of 1.5 Volt DDR3 800/1066/1333 DRAM, 16GB Max. Right now you have 2 gbs (2x1) configuration of dual channel memory. It is best to add the same kind of memory to keep your dual channel status. If you were to add slower ram than your current 1333, all dimms would be downgraded to that slowest speed stick. So if you added a 1066 stick to a pair of 1333, you would end up with 3 1066 sticks. I think something like 2x4 or 2x8 would suit you best of 1333mhz ram with low timings. Please remember that 32bit Windows 7 has a limit as to how much ram it can use ~3.5gbs, as opposed to 64bit, which does not. But I see you are using 64bit so you're good to go. There are a lot of different PC3-10600 types of ram to consider depending on the amount of cash you want to spend. If you ask 5 people what kind of ram you should buy, you will get 5 different answers.