Might want to see my response to the other thread (http://www.tomshardware.com/forum/25742-43-linksys-befw11s4-router-admin-page),
I assume your question is related.
Firmware upgrades are not all that difficult. But I sure hope they're not charging you for it, because it's probably not worth it. But if it's free (and usually firmware updates are), you typically use the webadmin interface to load a binary file and apply it. Just make sure to do it over a WIRED connection, never wireless! And doesn't hurt to have the router on a UPS as well. Worse thing that can happen is to have the power go out during a firmware update. It could brick it, i.e., turn it into a fancy paperweight.