You can only delete your Auction up until the Reserve Price has been met. If there's no Reserve Price set, then the Auction can be deleted up until the first bid has been placed.
If you want to delete an Auction in your account, go to your dashboard and navigate to Auctions. Use the drop down to select Auctions.
Then click on the red delete button next to your Auction.
You will be asked 'Are you sure you want to delete this record?' Click on Confirm to delete this Auction.
Your Auction will now be deleted.
The free or purchased Auction will be still be available in your account for you to reuse whenever you need to (unless expired).
Remember, if you want to keep an Auction in your account but hide it from view, you can Edit your Auction and set the Status to 'Inactive' and then Submit your changes. This means the Auction will still be saved in your account but it's no longer live and no bids can be placed.