If you want to delete a project, you should close that project first. 

After that, open the "Closed Projects" page.

Open the project. go to "Project Settings" and open the "Advanced" tab.

You need to write down the title of the project in the box, so you could delete the project.

he owner of the project is the only person who can delete it. If you are not the owner, you can leave the project.​

You could export projects before deleting them.

If you delete your project, you can't undo this action. 

After deleting a project, all of its data will be deleted and you can never have access to them.