If you still have access to your admin password, you can change the WEP key in the router settings, accessible by navigating to your home IP address (usually 192.168.1.1 for Linksys routers) in your Internet browser. Alternatively, if you do not have access to your admin password, you can manually reset your router and set up a new WEP key.
If you have forgotten your WEP key, but not the password to your Wi-Fi router, you can change your WEP key by first connecting to your Wi-Fi router via your home IP address. Then, go to the security tab in the menu, where you can change the key.
If you have also forgotten the admin password to your Wi-Fi router, try the default ID and password to your router. This is often found on a sticker on the router or in the documentation that accompanied the router in its original box. If you cannot find these, or if the provided defaults do not work, reset the access point via the hardware of the router by inserting the point of a paper clip, or something similar in circumference, into the small hole on the router. If you are having trouble with this maneuver, find additional instruction in your router's hardware documentation.