FamilySearch Family Tree is a great source of information. It is one of the first places I turn when doing a survey of previous research. Unfortunately, not everything in the tree is correct. I can fix an error in the tree when I have done thorough research and have strong evidence to contradict a relationship in the tree. What is the best way to do this?
The BYU Family History Library has posted a video from Kathryn Grant about this very issue: Getting Relationships Right in FamilySearch Family Tree. The presenter gives a great overview of Family Tree. She shows how to add a spouse, fix a spouse relationship, add a child, and fix a parent-child relationship. She also has specific guidance for fixing a looping pedigree, where an individual is shown as, for example, the child and parent of the same individual. Throughout she shows examples of good reason statements for her changes, nothing too complex, but more than just “incorrect relationship.”
I also learned that this edit symbol is a way to edit relationships: 
Somehow I had interpreted this as editing the person’s information, but this is really only about relationships.
Unfortunately, after I used the information from this presentation to make a fix, another researcher undid my latest fix. This was done in spite of the fact I added informative reason statements. Working with (or against) other researchers is what comes with FamilySearch’s single Family Tree format. But at least I now know the best way to make the fix.
Liane Jensen Research 