Sorry you want to leave us. Please note that after deleting your account, all your data, such as your contacts, will be erased irrevocably.
To delete your account, please go to the master data in your login. To do this, click on your profile icon at the top right of the menu bar.
Click the Delete Account button at the bottom of the page...
...and confirm in the pop-up. This is the final step before your account is deleted permanently, so make sure that by this point you have recovered all data you still need.