Changing the Password on a Cisco Wireless Router

My roommate gave our wifi password to our neighbor.  Now, neither of us can connect to the internet for very long without being booted off.  I want to change my wifi password, but I can't figure out how to.  I've tried everything I can think of and find on Google, but nothing has worked.. the password remains the same.  I tried calling Cox, but they were of absolutely no help, nor was Cisco customer service.  Has anyone else figured out how to change the wifi password on a Cisco wireless router?  If so, I would greatly appreciate step-by-step instructions.