First, be sure you want to change, rather than reset your password. If you have forgotten your password and need a new one created for you, you need to reset your password by clicking “Forgot Password”. Instructions for that are here.
If you know your password (or have just been assigned a long and complicated password by the system) and want to change it, enter your username and password as usual. Then, instead of clicking “ChildWare”, select “Update Account Information” and follow the instructions to change your password.