Bare in mind, when reconfiguring the key that you have to do this from a wired connection and if will not work from a wireless one. Since you didnt say what model you have i will have to generalise.
1. Make a connection from the router to your PC (through the LAN port)
2. Open your browser and type 192.168.11.1 in the address bar and press enter
3. Enter the username "root" and no password (leave it blank)
4. Click wireless Encryption => Select the encryption type and enter a new key and click apply.
You will now have to enter this key onto your laptop when connecting to the wireless network.
If you get back to me with the specific model number i can go into more detail and give you an exact walk through if you still need it.