You can't, that option is disabled/hidden (same as account signatures).
It should be inside account perferences (above logout)...even https://hub.virtamate.com/account/delete leads to nowhere.
EDIT: You are not allowed to change username...so what made you think that you can delete account...no-no!
You must accept this policy before using the site.
hub.virtamate.com
You may also send us an email at privacy@virtamate.com to request access to, correct, or delete any personal data that you have provided to us. We cannot delete your personal data except by also deleting your user account.
i mean that's on you if use usernames or stuff that leads back to other more personal accounts, there's not much anyone can do to help with that
but for deleting your vam account, it's explained in the privacy policy:
You may also send us an email at privacy@virtamate.com to request access to, correct, or delete any personal data that you have provided to us. We cannot delete your personal data except by also deleting your user account.