This is a two step process, and here I'm assuming that you are clever enough and you are hosting with a company that offers cPanel 
. On other hosting environments the process might be slightly different, but the basics are the same.
Step 1: Change your database password in cPanel
- Login to cPanel (Typically your cPanel address is something like http://www.yourwebsite.address:2028 or http://www.yourwebsite.address/cpanel).
- Click on "MySQL Databases" near the bottom of the page (located under a section called "Databases").
- Scroll down to the bottom of the page, to the section called "Current Users".
- Click on the Joomla database user.
- Enter the old password and the new password.
- The password is now changed, that’s the good news. The bad news is that your website has stopped working! You need to execute Step 2 immediately to get it back up!
Step 2: Change your database password in Joomla
- Connect to your website through FTP.
- Download the file "configuration.php".
- Open the file "configuration.php" in a text editor, such as Notepad.
- Change the "$password" value to the new value.
- Upload the file, and you’re done!
