Internet fast on one computer slow on another?

I just built my first computer yesterday and today bought a wireless adapter for it today. The adapter being a wireless n nano usb adapter DWA-131 I just tested it on speedtest.net and I am getting a fluctuating download speed of 1 to 5 mbps and upload of 4.5 to see how my uncle's computer would perform (being wireless and under the floor the router is in) he has a godly download speed of 22 mbps I am wondering how this is possible and if I could somehow fix my computer because if this is true it is seriously underperforming