Follow the instructions below to change email account's password.
Change Email Account password from cPanel
Step 1. Log in to the cPanel.
Step 2. Click on Email Accounts option.
Step 3. Clik on Manage option which is right next to your Email account.
Step 4. Click on GENERATE to generate default password or you can type password of your choice but keep in mind password strength has to be 100. Also copy that password and save in text file for future use.
Congratulations! You have successfully changed your Email Account's password.