Wherever you are in the Publicitymedia system, in the top right hand corner of the screen is a button with your name. Click on this to drop down a menu that includes a link called Change Password and go to the Change Password screen.
Then simply type in your new password in the first box, retype the same password in the box below and click Save. You have just changed your password.
Use this process whenever you need and want to change your password.