To change or reset the password for an email account, first log in to your cPanel:
http://www.yourdomain.com.au/cpanel
Once logged in, in the middle of the page click on Email Accounts
The email accounts page will now be shown. In the middle of the page is a listing of all your email accounts. To the right of each email account you will notice a link labelledChange Password
Click the Change Password link for the email account you would like to change the password of. Once clicked, a new section will be shown prompting you to enter a new password, and then to enter it again to confirm it. Once the new password you want has been entered and confirmed you can click Change Password