To delete a person's partner, without deleting the person, you will have to cut the link between them:
- Go to the profile view
- On the right, you have the family circle
- Click on the pencil
- The "Edit family circle" window appears
- Click on the scissors to the right of the partner
- You must confirm your choice
- Click "Yes, cut the link"

If there was a child, you might have to cut the link between the partner and the child as well.
It might also be necessary to delete the event "Marriage"

Watch our tutorial "Add partners and marriages to your tree"