To make someone else the owner or admin of a group you created, select the member list by tapping the Group Header or the vertical ellipsis
and then tapping "View Members"
Next tap the member you want to be the new owner or admin and then tap "Make Group Owner" or "Make Group Admin."
You will be asked to confirm that you want this individual to be a Group Owner or Group Admin. In addition, you can revoke Group Admin rights but tapping the users profile and tapping "Revoke Group Admin Rights"
If you transfer ownership you will be made an Administrator. You can now leave the group without the group being deleted for everyone.