If you'd like to disconnect your Facebook login from your PopItUp account (if you'd like to connect it to a different account, for example) just head on over to popitup.com/accounts/social/connections (which you can also find from your Profile -> Social Account Connections), select your Facebook account and click "Remove".
That's it! Your account should now be disconnected.
Note that disconnecting your Facebook login from your PopItUp login will not have an effect on the connection PopItUp needs for consultants to post photos to Facebook.