Step 1. Go to Admin –> Manage Users –> View All –> Approved Users –> All Blocks–> Search for the user whom you wish to deactivate.
Step 2. Click on Edit button.
Step 3. A separate window pops up. You can see the multiple flats listed where the user is part of.
Step 4. Click Delete for the flat where he is no more part of.
Step 5. Click Save Changes.
Note: If you wish to deactivate the user account for all the flats go through the link here, http://faq.apartmentadda.com/how-to-deactivate-the-users-who-has-sold-and-left-the-flat/