In Control Panel>User Accounts, you can add a new account and call it what you like then add a password to it. If you want to changetyhe login and password for your wireless router, look at the instruction manual or start by pressing the hard reset switch. Then you need to access it to change the login details. If unauthorised or suspect people have used your network, it might be wise to change the SSID (network name) and security key and then to hide that SSID from the outside world.
Post back if you need more details on that.