You can only delete Users with a Draft/Invitation Sent/Invitation Expired Status.
To delete the User,
1) Login to your Board.Vision portal as an Administrator*.
2) From the left navigation menu, go to Users.
3) Search the Username.
4) Click on the Username.
5) In the View User Basic Information page, click on Delete.
6) Once a Delete User window pops-up, click on Confirm.
* This feature is available depending on your access level.
Please refer to Administrator Access Rights Matrix for more information.