If you build your family tree in Family Tree Builder, please read the following article: How do I delete a person in Family Tree Builder?

To delete a person in a family tree created directly on MyHeritage.com click on the person card and then click ‘Options’ > ‘Delete this Person’.

Please note that a scenario where the deletion of a person disconnects another person or a branch from the rest of the tree, is not allowed and the deleted person will be marked as ‘unknown’ instead.