If you've taken a video upside down, no worries. Flipping it back up is easy by using the free GoPro Studio software.  Here's how to do so:

1.  Import the files you want to rotate into GoPro Studio, by using the "Import New Files" button.  

2.  Highlight the video that you want to rotate in the import file list on the left hand side.

3.  Check off the "ROTATE/FLIP" box on the lower left hand side of the viewing screen.  This will rotate your video 180 degrees.

Once you have completed these steps, you can make any additional adjustment, such as trimming the clip or changing frame rates before converting and then exporting the file.  Once you have exported the file, all the changes that have been made will be saved in the exported file.