On the Menu bar across the top of the screen go to Others > My Account > Password
Enter the old password then enter and confirm the new password and click on Change Password to save the change.
Click on the Settings icon (top right hand corner next to Logout) then choose Password from the menu on the left. Enter the old password then enter and confirm the new password and click on Save to save the change.
Unfortunately at this time you are unable to change the email password from within the webmail system, you will need to change it using your Domaincheck control panel.