To disable a user, follow these steps:
1. Go to My Account
2. Go to the Users page, under Admin Only Options
3. Enter the name in the Enter Name field and select the user
4. Click the Actions button to see a drop-down menu and select "Disable Users"
5. Select a reason for disabling and click the "Disable User" button
You may also be interested in:
Re-Enable a Disabled User
Add a New User