Deleting your Windscribe account can be done with just a few clicks on the Account tab of your My Account page here: https://windscribe.com/myaccount/account
Scroll to the Danger Zone card at the bottom of the page and click Delete Account:

A Delete Windscribe Account window opens:

Enter your current password, tell us the reason for deleting your account, and click Delete Account (it stays disabled until both fields are filled in). If you are on a paid plan, any time left on it is lost and cannot be refunded. Once you confirm, your account is deleted and you are signed out.
Keep in mind that this is a permanent action so recovering the account once it is gone is NOT possible.