change linksys wireless router password

How can I change the password for my linksys wireless router from the default one?

 

First of all which model do you have?
Despite that try this:
Open up your web browser and type in http://192.168.1.1
Login using the default admin username and password and then click on the administrations tab.
You should now see a gateway access section which asks for a username and password, this is where you fill in your new settings and then save settings at the bottom. If this doesn't help then providig your model number would help.