The open-login plugin allows you to connect 2 different accounts, for example your local q2a account with your facebook account.
To be connected they must be associated to the same email address.
When you login for the 1st time with your second login (e.g. Facebook), the plugin will ask you if you want to connect it to your existing account (your local q2a account).
Just confirm it.
Pay attention : all the data (points, posts...) of you existing account will be lost.
I think this is an issue that should be solved, because when I want to connect 2 accounts I want to mantain my data and not to loose them.
I've already opened an enhancement request for it.
But it looks like that there are some technical issues to merge two accounts in q2a.
However you can watch it here :