To disable a user's account:
  1. Navigate to CORE > People finder
  2. Search for a user
  3. Select the Access tab
  4. on the right side, locate: Disabled/Locked
  5. Select Yes

A Platform Manager can go back into the account at any time and unlock the account. 

Disabling/Locking an account does not change or remove any of the user's information from the system. This simply prevents them from logging in.