tarotheaven, don't panic! Everything can be solved easily
The first question is — where exactly do you want to change your nickname?
- To change the username on uID.me and all the further uCoz sites you will log into, go to uid.me, log in, and edit the Username field in the settings of your profile;
- To change the username on your own website, go to its Control Panel, select the Users module, search for your username, and click on the icon next to your name (if you use the old Control Panel);
- If you want to change your username on this forum, send me a private message with the new username.
Unfortunately, the only way to change your username on the uCoz websites you've previously logged in to is to ask the owner of the website privately.
I can't imagine how or why my password would be my facebook password
This is a general process of social media-based authentication. It is done like this on most of the websites that support social login. What else would be the point of social login otherwise?