If your router is compatible with software such as DD-WRT you can flash your router with better software than it comes with to start with, but that it also allows you to boost the physical power of the amplifier from inside the router.
Make sure to do some reading on the correct levels to set this as since it's very similar to increasing the voltage to PC components for overclocking it will cause additional heat build up. If you wish to boost it substantially you will want to open up your router and install a custom heatsink that's better suited for the additional load.