Choosing wireless LAN adapter for pc?

Changing to N would not increase the signal - A/B, G & N are simply the speed in which the data travels (and even with an N adapter; everything else needs to be N capable as well to archive the best transfer speed). A repeater is the best route to go. It is very easy to add an access point to your current configuration and most home routers/access points make this easy through their administrative wizards. Good luck.