There is something in the FAQ and free for all to read. No need to waste the time to explain everybody how this website works.

How do I delete a giveaway if I create one by accident, if I select incorrect information while setting it up, or if the gift is no longer available?
When viewing your giveaway, you'll see a "Delete Giveaway" button in the left column. Clicking this button will let you specify a reason for the deletion, and it'll walk you through the process of creating a support ticket. If the giveaway is still open, the ticket will be automatically approved and the giveaway removed. If the giveaway has already ended, then the ticket will need to be approved by a member of support.