You can easily change your email password by opening your cPanel account → Email Accounts section:

Next, locate the email account from the list and and click on Manage:

There, enter a custom new password for your email account or click on Generate to create a secure password automatically:

The password must contain uppercase and lowercase letters, numbers, and symbols. Once done, scroll down and click on Update Email Settings:

That’s it! Now you can use the new password to log in via webmail, as well as to set up any email client.
Additional Resources
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Manage Email Accounts – cPanel Official Documentation