The power output of consumer wireless routers is limited by design to avoid signal congestion and although slightly more powerful models are available they rarely make much difference to your wireless connection.
Part of the problem is that wireless data flows in both directions, so while increasing the router’s output means that PCs, laptops, tablets and smartphones receive a stronger signal, there is no improvement in the strength of the return signal, from the device to the router.
Repeaters or extenders can definitely help, but only if they are installed strategically around your home, and it also helps to use an external USB wireless adaptor on the PC or laptop, preferably one with an external antenna.
Relocating the router – higher is usually better – and connecting it to a more efficient or directional antenna can also improve coverage but to determine the best position you need a Wi-Fi signal strength meter. If you have an Android smartphone there is an excellent free app from Google Play, called Wi-Fi Analyzer. This quickly shows how effective each change in location is, and helps to identify dead spots, where a repeater can do the most good.
Other things to check include accessing the router’s setup menu to make sure that it is using the more efficient 802.11n standard. If you are experiencing weak or noisy signals this may be the channel that your router is using so while you are in the router’s online administration interface try changing the channel to a different one. (Wi-Fi Analyzer can show you what channels are free).
Finally, make sure there are no other wireless devices or noisy appliances close to the router, which may cause interference. If so, move the router as far away as possible.
If you decide to buy a new Wireless Router make sure that it comes with a built in ADSL Modem so you can plug it into your telephone point.