Below guideline will show you how to change Database password in cPanel
1) Login to your control panel domainname.com/cpanel or domainname.com:2082
2) Go to MySQL Database
3) After that go to the below of the page that will show Current Users and Click on the database user
4) You will get a page like below and may proceed to change the Database Password.
5) Lastly, click on Change Password.