The Admin Console is located under the options within your User name in the top right, and is only available to product admins (not contributors). 

To remove users from within the Admin Console,

  1   Select your desired account in the upper left.

  2   In the user list grid, select the check boxes associated with the users you'd like to remove.

  3   In the list of icons, choose Remove Users.

  4   Select Remove.

Removed/deleted users no longer have access to the account or any associated projects.