How to remove your Digg account
As can be read on https://about.digg.com/faq it is impossible to automatically delete your account. You should ask them using the webform named on this page.
Direct removal link: https://about.digg.com/contact
Helpful Trick: Removing online data
Publicly visible text/images often aren’t properly removed even when you succeed in removing an account. Try editing or removing them manually before removing the account itself. If you’re unsure what happens to your tracks: this can be found mostly in the Terms of Service/Privacy Policy; otherwise you can always contact Digg and ask personally. By the way, removal requests don’t necessarily mean your data will actually be removed (e.g. due to legal obligations).
Helpful Trick: Remove third-party logins
If you signed up for Digg using a third-party login such as Facebook or Twitter, you probably want to revoke all access from Digg. Click here to find out how.