If you'd like to disconnect your Facebook login from your Sonlet account (if you'd like to connect it to a different account, for example) just head on over to your account Settings.
Scroll down to the bottom of your General Settings and click Social Account Connections.
Select your Facebook account and click "Remove". It will look something like this:
That's it! Your account should now be disconnected.
Note that disconnecting your Facebook login from your Sonlet login will not have an effect on the connection Sonlet needs for consultants to post photos to Facebook.