Account deletion is not yet implemented (but it seems they are working on it!). In the mean time, they can do it manually for you.
Go to: http://adf.ly/contact
Choose “Other” test as a subject and ask them to terminate your account.
They will more than happily help you. Note that it can take up to three days for them to respond.
URLS:
http://adf.ly
http://adf.ly/account/delete