If you edit your tree online, please read the following article: How can I move a complete branch to a different place in my online tree?
You may find that an entire branch is in the wrong location in your family tree.
For example, person A and all his descendants may be under person B, when they are really the descendants of person B’s brother.
In this case, use the Detach function to disconnect person A from his parents.
Then use the Attach feature to connect person A as a child to B’s brother.
You can read more about how to use the Attach Detach feature here: