Is there a way to change my Spotify login from using Facebook to using just email and password?
You can do so by disconnecting from Facebook. The following instruction shows how to do this:
Disconnect from Facebook.
Since you have a dedicated Spotify account, disconnecting from Facebook is easy.
In the desktop client:
Windows - Go to Edit > Preferences > Social Network > Disconnect from Facebook.
Mac - Go to Spotify > Preferences > Social Network > Disconnect from Facebook. Once you have done that, your Spotify account is no longer linked to Facebook, you need not continue any of the steps below.
You may find due to data caching in the client, that you still see Facebook information (such as the People list) hanging around, a quick clean reinstallation of the application should fix that for you.
If you can't see the option to connect/disconnect, then you are logged into a Spotify account created with Facebook not a dedicated Spotify one.