Distance or speed? My understanding is that you can't do much about the speed but you can buy repeaters to place around your house/office to make it available further away.
I believe he's talking about the distance. There are loads of actually working WiFi Amplifiers. You can have a look.
generally distance issues are a result of a bad router. Most of what you'll find at your local stores for hardware isn't good. Personally i've owned every router that walmart and bestbuy offer and find the prices to be not on par with the quality of what you're buying. First thing you need to assess, is how much distance do you need, is your current router crap, do you have a lot of interference in your location. If money is an issue: First look at the placement of your router, it should be in a central location to the 4 corners of your building/home for maximum coverage. Avoid setting it around a brick, metal, or other devices that transmit signals. brick and metal both block signals and other transmitting devices can corrupt signal strength and quality. depending on your router and wifi on your laptop/pc you can likely crack them open and add an antenna onto them for extra db gain. Prior to doing that, you should first make sure that the wifi/or device is actually good. If money isn't an issue: Mikrotik RB951G-2HND 5-Port Gigabit Wireless AP 1000mW $78.64 Mikrotik Routerboard RB2011UiAS-2HnD-IN Sfp Port plus 10 Port Ethernet $119.49 Both of these are the best consumer grade routers you'll buy, they run RouterOS and are a lifesaver when it comes to dependability. the most expensive router i've bought was around $400, yet the $80 Mikrotik runs laps around it.