1) Login to Joomla admin panel.
2) Go to ‘Components’.
3) Click the option ‘Admin Tools’.
If you are not installed the Admin Tools, please use the following steps to install.
a) Download the stable version of Admin Tool to your system.
b) Go to Joomla admin panel >> Extensions >> Manage.
c) Browse the Admin Tool file under the section ‘Upload and Install Joomla extension’.
d) Click ‘Upload and Install’ button.
4) Find the icon ‘Password Protect Administrator’.
5) Enter the username and password.
6) Click the button ‘Password Protect’.