you need a2 uploader to install it. the higher the f/w number the more features and more bugs fixed (i think). in your case it's #42. but you need other things like FS and customize_upgrade.xml. otherwise it will screw up your icons and disable access like your sms inbox. i just know the FS and the f/w you get (also known as MAIN) must match. dont ask me about the xml file, im still trying to produce mine.

in summary i think the xml file will fool SEUS so you can use the new f/w even if the f/w is not for your country (possible your country latest f/w lacks features of a new f/w for another country, i dont know)

maybe the experts can confirm.