mikec

when you say accessing "it" what do you mean? the router's admin function or the internet?

use IP Filters to filter out the IP of the computer you don't want accessing the network/internet, or as firebirdta said, block based on the computer's MAC address.

use a better password to prevent the user upstairs from logging in to the router admin

__________________
Until the 20th century, reality was everything humans could touch, smell, see, and hear. Since the initial publication of the charted electromagnetic spectrum, humans have learned that what they can touch, smell, see, and hear is less than one millionth of reality