If you have admin rights, you can deactivate accounts under your company as needed.
Follow these simple steps:
Go to Settings, and Open Company Settings
Click Edit on the top right
Search for the user or users you need to remove and click on the X next to their names.
Read the confirmation message and click Confirm
NOTE: You also have the ability to reset user passwords from here as well.
There may be times when you do not want to deactivate the account, but rather change the password to access it. You can also have multiple admins in a company and whoever has admin rights can add/remove this permission to other accounts.