The complete deletion of a project is not possible. Only the project's contacts and values can be deleted, but not the project structure, fields, messages, forms, etc. If you don't use a project anymore, you can archive it to remove it from your list of active projects.
Warning: Deleting the list associated to a project causes the deletion of all related contacts and statistics. The deletion is final, NO RECOVERY is possible.
How To
Go to All projects, then edit the project you want to delete:
The project must be online, thus showing 
.
Scroll to the bottom of the list and click Delete list:
Confirm by typing DELETE as requested and click Delete list:
All contacts in the project, the contact information and the related statistics will be deleted from the database and the project's status will change to 
(in preparation).
If you decide to reuse the project later on, you will just need to build it again. The structure will still be there, but you will need to import contacts and values from scratch, as they were deleted.
**Note: Once the list is deleted, allow 48 hours before your contact count is reset to zero.