I have a low wireless signal with a 802.11n?

ok so i recently got a BR6226N Edimax Router, this supports 802.11N and i have an Asus PCE-N13 802.11 b/g/n Wireless PCI-Express Adapter. I cant get good connection to the router even though i am about 10-15 meters away, its through 2 walls one is brick but there is a window next to it, i have no clue why i have bad connection! do i need to change some settings or something on the router or on the wireless card? with the wireless card it was previously connected to a 802.11g so could some settings be in place?