Why? You must be fully satisfied before doing this as once closed you cannot re-open, so I hope you are not relying on a Promise of a refund as once closed promises are easily broken.
Go to your My eBay > Messages, click on the return message from ebay and then click on the blue "See return details" tab. Near the top right of the next page, below the blue "Reply to seller" tab you should see - "If you no longer want to return this item, you can close this return".
