Anyway, the instructions (or firmware/software) that come with most routers is limiting and does not give you all the options a professional router might have as far as bandwidth monitoring, bandwidth control, and other stronger security options. Not all routers are upgradeable. In fact, recently home router makers are now building their routers as not to be upgraded. You almost have to get a premium router to have a chance a getting the extra features. One of the most popular routers is the wrt54-g(l) from Cisco Linksys. When I see one at a resale store, I think about getting it. Most firmware sites will have a listing of what can be upgraded with their firmware.
There are several ways to upgrade firmware. All of them entail uploading or sending a file to the router to replace the existing software in it. The most common way is to upload a file via the web interface on the router. That is what we will do. Some routers may require a tftp server to send the remotely to the router and is a bit more complicated. The most complicated install is a redboot which requires special communication with the router. These can be the most challenging. I have done one and prayed all the way through it.
NOTICE: Have a pencil and paper to write down any settings or options that might be needed later. This project could render your router useless. If you are unsure, please get a professional to help before starting on it. I will not be responsible for any issues, You do this at your own risk.