Did you buy a wireless NIC that is installed in the PC with an antenna sticking out the back? If you did and your PC lives like most people have it stuck inside a cabinet then the signal might have a hard time getting to it. I always recommend a USB cabled wireless adapter like this.
That way you can move it around some and have it higher than your PC.
The cheap things to do is get your router physically higher, this will help get the signal broadcasting a little better. Do a google search for windsurfer antenna. I know it looks dumb but if you poke around you will see posts people have made about getting a signal boost from it. Put it on your routers antenna and the antenna on your PC. Even if you only get a bar out of it, its paper and some tin foil.
There are more expensive things, signal boosters and the like but I'm cheap and always start there. =)
Oh and to answer your actual question: I know of no setting that will make the signal better. If the router is a N and your wireless adapter is N you could try just setting the router to just N instead of b/g/n like most do out of the box. It might help but it should be using N anyway if your adapter is N.