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
Manage Email Accounts - cPanel Official Documentation