How do you connect your PC to your router? Reason I ask is that your router will automatically negotiate the fastest connection speed your phone line can manage. A new router will not be able to connect any faster.
If you connect to your router via an Ethernet cable, you get all of that speed as Ethernet is a very efficient way of transmitting data. If you connect via home plugs, you lose a percentage of that speed due to losses in the transmission method. If you connect via WiFi, it's even worse.
So before you consign your router to the bin and waste any money, make sure you have a direct wired Ethernet connection to your router.