To remove a person, click on them and the choose the "More Options" button on the sidebar. This will show you more options (shocker, I know), and one of the last ones should be "Delete [first name]".
However, this only works when this doesn't take away someone else's connection to the tree - if you delete someone who has a partner who isn't connected to anyone else on the tree, or has parents or children that no one else is related to, you need to delete these people before deleting the person in question (otherwise, the "Delete [first name]" button just won't show).
Hope this helps!
