A student's password can be changed by either administrator or the student's parents. Here, when the parent wants to change their child's password, first select the child's name from the top right corner drop-down list of the parent portal (in case there are multiple children associated to the same parent). Then, from the portal's menu panel select Students >> Change Password. Enter the current password, the new password and re-enter the new password before saving it.
The student's portal access password is changed and now the student will need to login with the new password set by the parent.