Hello! Deleting is sometimes a bit tricky, as you can't delete people if that means others would lose their "connection" to the rest of the tree, i. e. you can't delete a parent if their children wouldn't be connected to anyone anymore, and you can't delete a wife if this means her husband would hasn't any other connection to the people on the family tree. To solve this, you'll need to delete these people (in this example children or partner) first.
If you just want to start over, it might be easier to just create a new family tree (especially if your first "failed attempt" includes a lot of people, so that manually deleting would take some time). To create a new family tree, you need to go to "My Account" (on the upper right side of your screen, next to "Save" and "Log Out"). On the bottom of the "My Account" page, you can choose to "Create or import new family" (and also remove the old tree from your account).
Hope this helps!
