Log into your router and change it. But since you have not told us what your wireless router is, it's hard to help here. Most home routers sit at http://192.168.1.1 or http://192.168.0.1 or maybe http://10.0.0.1, etc. The exact address is can be many things and if it was changed, look at the default gateway in your TCP/IP settings on your computer (if Windows, "ipconfig /all"). Try the default userid and password as documented by your router's manual. If that's been changed and you don't know it any longer, then you will have to resort resetting the router to factory default settings, see your manual for details.
I need to change my wifi internet password also, because my neighbors are using my internet. How do I do this? I understand I need to log in and change the router, but I'm not sure where to even start. Could you walk me throught his process please?
Type one of the URL's in the message above into your browser. If you have the right address, a page with a login prompt will appear. Type in the admin userid and password (whatever they are, consult your manual for the defaults). Once in, go to where the wireless options are configured and change the password. I can't give explicit instructions because I have no idea what router you have and they are all different. But it's usually very obvious, the menus and tabs are usually based on functional areas. When in doubt, consult your router's manual, it will have explicit instructions to both access the admin interface and change the various settings for the router.
also if u have the wireless gateway the smc or arris and u have never set up ur network or changed ur password from what it is when u first got the device then ur password is on the sticker on the bottom of the modem next to network key