In the portal:
1) Open your portal and locate the Users menu on the left sidebar.
2) Once in the Users tab, you can locate the user by using the search bar.
3) Then click on “Search”, your results will appear in the user's list below the search box.
4) Locate your user in question, then click on the three dots at the far right.
5) Click on the “Delete” option from the menu that appears
6) A confirmation message will appear, click “Delete”