Question about dual channel RAMs

Right now l have 2x2Gb installed in my PC. My CPU fan is blocking the 1st slot so l cant insert a module there.

I want to upgrade to 8Gb of total RAM. So my question is do l buy only one 4Gb module or replace the 2x2Gb modules with one 4Gb module more

so l wont lose the dual channel?

The second option, just get 2x4 GB, it's cheap, and you get to keep dual channel, go with something like this:

http://www.newegg.com/Product/Product.aspx?Item=N82E16820231546

The sticks I linked have low-profile heatspreaders, so they may even end up fitting under that cooler's fan, if you want...

Also, pay attention to the RAM slot coloring scheme, should be listed in your motherboard's manual, to get dual channel, sticks need to be placed in the same colored slots...

You should ask this in the PC hardware forum. :)