Short and quick directions:
1.Make sure the battery is FULLY charged.
2.Download the updated firmware file HERE.
3.Double click that file and RUN it. This process will spit out the actual firmware file.
4.Place 'spit out' file on ROOT (in no folder) of your SD card and put card back in your GH3.
5.Turn GH3 on and press the play button (the little green play arrow to the left of the EVF).
6.You'll see the GH3 asking you to update. Select YES.
7.It'll go through the process which will take between 3-5 mins. When it finishes, you're done.