Not sure where you get the 50mbps number. If you hook up to the lan ports via ethernet you should get close to 100mbps. That router only has 10/100 ports so even if you had 200mbps internet you would still only run 100mbps. There is no limit of 50mbps that I know about the router should easily run 100mbps.
On wifi it is much harder to say how fast it will run. It is actually a combination of the router and the end device. This is a so called "300" router. In some magic world you could get 300mbps. You will not get anywhere near that. If you put the end device directly on top of the router you might if you get lucky get 100mbps. At more normal distances from the router it the 50mbps number you see would not be...