Please refer to this article that will teach you not only how to delete duplicates but also how to merge them and fix your family tree: How do I merge duplicates in my online tree?
To learn more about this topic, read this article on the MyHeritage Knowledge Base:
How to Delete Duplicates from Your Tree. On the MyHeritage Knowledge Base, you'll find additional articles, webinars, and how-to videos that can help you master your genealogy skills.