IIRC if you set your password & then forgot it, hold the reset button down for 15 or 20 seconds to reset everything. Then at the login screen leave the user ID blank and leave and enter admin as the password. After you're in, go to the administration page & then change the password to something you can easily remember from now on, like smglover16 .
Depends on the router. Just helped someone with similar issue. Typically open your browser and go to 192.168.1.1. If you've changed the password, try what was suggested by fazers. But the default username and password could be different. I've seen default username = admin and leave the password blank. Also, try default username = admin and password = password.
Or, give us the exact model name & number of router. Then someone can google for the instructions online and look up the default username and password if it's not one of the ones listed so far.