1] Login to the admin site.
2] Click on ‘Users’ module and select ‘User List’.
3] Select the particular user/users whose status you want to change from ‘active’ to ‘inactive’, just click on the active icon.
4] After this you will get an popup message regarding the confirmation for proceeding, click on ‘Yes’ button.
5] The work is done, now the particular user cant able to login from the frontend.