This guide is for those of you on a Windows machine. Mac users, I have no idea what to tell you.
To start, we need to figure out what your IP address is. The quickest way to do this is to press Windows Key + R (Windows Key is beside left-alt). In the run box, type cmd and press enter. You should see a black box now with a blinking cursor. In this box, type ipconfig /all and press enter. Look for "Default Gateway" note this address down. Mine is 192.168.2.1 so we'll use this as the example.
Open up a new browser window or tab, and type in that IP address exactly as you noted it. You'll get a login notice, and this will differ depending on what router you have. Go to this website to get your default username and password: http://www.routerpasswords.com/.
Once you have access to your router, again, all of this will differ depending on the make and model of your router, but you need to look for a wireless tab. Once there, you need to look for something that says "Channel" or sometimes "SSID and Channel" (SSID is the name of your wireless)
After you have found the channel tab, use it to select a new channel. I've read that anything betwixt 1 through 4 works the best.
This is a vague walk-through, so please ask questions and I'll be sure to help.
:EDIT: Here's a good reference site for routers - http://www.portforward.com/