Router download speeds are slower on Nighthawk R8500

I recently upgrade my internet service up to 100mbps from 50mbps.  After getting everything switched over i did a speed test and saw that my speeds were the exact same as prior to changing.  I did the test on several devices and even hardwired to the router and everything was the same.  I then hardwired directly into the modem and did a speed test and upon doing that saw that i was infact getting the correct speed.  Why and what do i need to do to get the speeds i am paying for to passthrough the router?