download a program such as 7-zip(
link), then install that, right click on the .rar file and click 7-zip and extract to... and select somewhere on your pc, then you should have a .apk file, this you can just copy over to your edge with a USB stick or over the provided USB cable and then install through ES file explore. You will need to be rooted first though, for that download the z4root app from the amazon appstore(or I can send it to you if you can't access amazon), and then use that to permanently root your device.
the build.prop is a file located in /system/ and is used to define various things about the device and its firmware build. There are a few guides around, you can find mine here:
link step seven is what you want.
Hope this helps!