Wireless N adapter but wireless B speed.

Hello every one, I am new to Linux and Ubuntu and I am loving it.
Everything works perfectly. I have wireless N adapter Tp-link model- WN821N and a net gear wireless N router. They only connect at max speed of 54 mbps and not higher. I searched the Ubuntu website and it says the adapter is supported out of the box and have all the proper drivers installed. Which is true because the thing works seamlessly but at a slower speed.
Please help.