For a start it's old enough to flash with Tomato (
http://www.polarcloud.com/tomato) which you should do immediately, the Linksys firmwares are pretty awful in comparison.
By channel number he means the radio channel that the router is transmitting on, some channels tend to be busier than others with a lot of routers by default using the same channel. Tomato has a wireless survey function which will allow you to find a clean channel. Otherwise using the Linksys firmware its a case of trial and error going through each of the channels till you find a clean channel that doesn't cause you problems.