Method 1: If you know the current password, and want to change it.
Firstly ensure you are logged into the Account.
Then, go to "My Account -> Profile" and you will find a "Change Password" check-box at the bottom of the screen.
Select the check-box to be presented with the options to change, then press "SAVE" when completed.
Method 2: For when you have forgotten your password
Use the "Forgot Your Password?" option from the primary Login page, and then follow the prompts.