It's really up to you, a new router would be helpful since it will be more up-to-date and will probably give a better signal at a better distance. However you could always try updating your router to get the latest updates, which could solve a lot of issues.
Another tip is that wireless signals are usually stronger when going down, for example, when the router is above you, the signal would be better than if you were a floor above it, that's why most large buildings with Wi-Fi will have their wireless receivers on the roof to amplify the signal downwards.
Also check that your wireless band (for some routers) is compatible with slower devices, so 2.4GHz instead of trying to make the router run at 5GHz to increase wireless speed, since a lot of devices don't support 5GHz speed.
Hope this helps a bit :P