you can't [yet] Undo a merge. What you want to do is move forward. I see that indeed you presently have four parents. As they have completely different names, i presume that this merge is incorrect.
In that case, the thing to do is to open the tree for the WRONG parents, and add a "brother" for yourself, with the names in the profile you merged with. You then open your OWN profile, and press the "Edit Profile" link on the right side. Select the Relationships tab, and wait a few seconds. You should see a list of relationships, put a checkmark next to the WRONG parents, and press the remove button. Press save, and you should be done.