In the login menu type admin (mostly)
and your router password.
In router menu opened in ur browser in setup to to wireless, there u can change ur security key. Also in internet menu u can change ur password to connect to ur isp (it depends on who setup ur password, you or ur isp, either way u will have to call up your isp).
Resetting will change everything to factory settings. Do this only if u know how to setup everything from scratch again. Best is to call ur ISP