Log into the Control Panel from Pro-webdesign.
You should see the main page where you can choose in the "Email management" box "Add / Remove E-mail Accounts"
Please note: the actual interface controls available depend on what package you have bought.
Administration of the Email accounts
Now you should be directed to an email admin page where you can "Add, Delete and change email accounts.
At the top is where you would add a new email and at the bottom is where you can administrate existing emails.
On the email you want to change the password choose from the dropdown box "Change Email Password"
Changing the Email Password
Simply enter the new email password twice into the boxes and it will be automatically changed. Note: you can also choose the "generate Password" which actually generates a very secure password for you.
P.S Dont forget to update your password in your email application.