Brand new gateway m-6846 vista 64bit

Question

i keep having to take my brand new laptop back 4 times in one week. they keep giving me a new one cause they dont know what is wrong. i did a little research and in 3 minutes i found the problem online. it says something about 64 bit vista not liking anything higher than 3 gb of ram, yet my brand new one comes with 4gb ram on it from factory. how can i fix this so i dont have to keep returning and can enjoy my laptop that i paid for. the blue screen keeps popping up. that is how i found the problem but i dont understand how to fix it? help