In My eBay go to Account > Payments, or on the hub hover over the Payments tab and select Summary. You'll get a big blue banner with eBay balance on it. Click the arrow on the right and it opens up a box where you put how much you want to withdraw.
Or here's a direct link:
https://ppcapp.ebay.co.uk/myppc/wallet/list
Click on the arrow on the blue box.
