You have 3 options for deleting a user. WOW, so many!
1. User Management(EASY ONE)-- Go to 'Insight' - > 'Community and Team' -> 'User Management' and then click the trash can icon next to the user you need to delete.
2. Org Chart(ALSO EASY)-- Go to 'Insight' -> 'Community and Team' - > 'Org Chart' and then hover your mouse over the user. You will then see a delete option pop up above there profile pic. Click 'Delete' to make them vanish.
3. Team Import(Deleting Multiple Users at Once)-- Go to 'Setup' -> 'Team' -> 'Import' -> 'Download Current Template'. This will download an excel sheet and the far right column is 'Action'. Type 'delete' in this column for the user(s) you need to delete. Save the file and upload it. This will also delete any user(s) you selected.
If you accidentally deleted a user, then check out this awesome article -> https://motivosity.freshdesk.com/a/solutions/articles/9000167336-accidentally-deleted-a-user