Replacing RAM Help

[Rinohsaw]

So i'm pimping out my old pc, replacing my 2x2gb ram (4gb) for 2x4gb ram (8gb). I know that their both ddr3, but i'm not into this hardware stuff and i'm afriad that everything's not matched up properly. What's suppose to match up so that the ram works properly? Here's my pc i'm pimping out: http://www.pcworld.com/product/585105/aspire-x3400.html and the website i'm going to buy my ram from (tell me what rams I should not buy if there are invalid ones for my pc) http://www.tigerdirect.ca/applications/category/category_slc.asp?CatId=3361&srkey=ddr3

 

[vortical]

Anything on this list will work:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007611%20600006126%20600006069&IsNodeId=1&name=8GB%20%282%20x%204GB%29