Changing the firmware with official tools is currently impossible but there are 3rd party applications which will help you install custom/official firmware on your phone.
First, you must root your phone to allow these applications to have access to the core system of your mobile phone.
One application which is developed officially and it's available in Google Play is Rom Manager. With this application you can safely install Android/Custom Roms/ Firmware or any other modifications available for your mobile phone.
Another solution is to use ODIN directly on your mobile phone. There is a PC version but this is safer and easier. Just head to Google Play and install the application on your phone. From its main interface, you can perform firmware operations regarding downgrading,upgrading or any other customization available.