When someone co-owns a project they uploaded with you, you don't have the ability to delete the project. You do however, have the option to remove it from your profile. To do so, head over to My Profile > Hover over the project you want removed > Click the Pencil Icon > Click Remove.
The project will be removed from your profile and you will no longer have access to edit it. However, it will still be visible on other co-owner's profiles.