Go to the My Broadcast tool, and select 'Preferences'. You'll see a tab marked 'Login Password, where you will be able to change your password.
This depends on your carrier, plan and phone. The cheapest way to do it is to set up email on your phone (almost all photo cell phones have it) and then send the pictures as 'attachments'. You can usually get an unlimited email plan for around $10 and then be able to send as many photos as you like!