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.
If you signed up for AdFly using a third-party login such as Facebook or Twitter, you probably want to revoke all access from AdFly. Click the icon below to find out how.