I have 256, and with games, adobe, ilfe I seem to be getting lag here and there. And no one likes lag so I figure its time for a Ram boost.

Im going to go third party because I can't see myself paying so much for apple's.

Would another stick of 256 be enough for me? And if I bought another 256 is the equal to 512 or does it mean 256 still?

Is it easy to install.... I've never installed a thing in my life on any computer hardware wise.

Also any recommendations, I'd prefer a local store I could go to. If not I am not object to a website though. Thanks.