You can change your password thru the control panel.   NOTE: Your password should be 6 - 8 characters long. Only printable ASCII characters are valid.  

For accounts created BEFORE Dec '06:

Select the side menu link "Site Management" and the "Settings" tab.
You can change the control panel/root password there.

For accounts created AFTER Dec '06:

Select the side menu link "Change Password" under the Settings section.

OR

Just click the "Set a new password" link on the welcome page
in the Site Management section. You can change the control panel/root
password there.