Adding to what Gloria said, if you are actually wanting to change how people are related to each other, click the edit tab near the top of the profile page. On the edit page, look at the column on your right. It will list the persons related to the profile subject. Below their names it will say:
Father: [Father's name] [edit]
Mother: [Mother's name] [edit]
Siblings: [His/Her name] [add/edit]
Spouses: [His/Her Name] [edit marriage]
[add/remove a spouse]
Children: etc.
Click on the edit button you need and you will be taken to a page with several options:
(For example)
A.) To set someone who already has a WikiTree profile as the father of [person's name] enter their WikiTree ID here:
B.) To create a completely new person as the father of [person's name] enter their basic information here.
At the bottom of the page, you can simply remove the person's relationship from the profile subject.
You can find more information about this at
http://www.wikitree.com/wiki/Editing_family_relationships
To emphasize what Gloria said, if you aren't on the trusted list, you'll have to contact the manager of the profile and she/he will need to make these corrections or add you to the trusted list.
I hope between Gloria's answer and mine, we've covered what you were needing to know.
