Wireless setup -> wireless network settings and channel box should be there. If you are unable to use the box, then uncheck the "autoscan" option.

As long as the router isn't faulty? You may find that something is interfering with the signal, other radio units, Phones, other WiFi devices can "Swamp" the receiver, The fact that even right beside it still isn't any good, & unless you can "up" the power level, (sometimes you can, check your manual) Then I am of the opinion that it is faulty. Ensure you have the latest driver for your PC's WiFi. too.