A side from getting a more powerful router/wifi card... if your router and/or wifi adapter have de-tachable antennas, you can upgrade those antennas to bigger ones(or a different type).
Most antennas are omni-directional(meaning they'll pick up a signal in any direction). However, they also make "directional antennas". Here's a page that describes it all a bit better if you care to read:
https://www.simplewifi.com/pages/how-it-works
I picked up a couple of 10dbi indoor directional antennas awhile back to use on my desktop that was pretty far away from my router. Tinkering with the direction of the antennas I was surprised that I was able to pick up the wifi from a Bestern Western hotel that's 8 blocks away from here.