It won't be one large file, it will be hundreds (or even thousands) of small files, depending on how often you tell the GoPro to take a picture and how long you let it run.
For example, I am dog sitting for my neighbor this week and I wanted to see what the dogs do when I'm not there. I set the GoPro up to take a photo every 10 seconds and let it run for about 3 hours 13 minutes. I ended up with 1202 photos. I used the 5MP picture size choice on the GoPro, which is still bigger than you need to do 1920x1080 video.
You didn't say what software you have available to you, nor what platform you are on (Linux/Mac/Windows), so it's hard to give suggestions.
I have Adobe Creative Cloud, so this is how I do it:
I used Lightroom 5 and imported the photos from the GoPro card through my USB card reader, about 4 or 5 minutes. All the photos totaled about 2 GB.
In Lightroom, I cropped all the photos to 16:9 (1920x1080 px), about 60 seconds. Then I exported them as JPEGs to a folder. This took the most amount of time, maybe 20 minutes. I watched the TV news while the photos exported.
In Adobe Premiere, I imported the 1202 JPEGs as an Image Sequence. Took about 10 seconds. In Premiere, you can export to just about any format you can think of. It even has presets for YouTube and Vimeo exports.
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I have a GoPro too, but haven't used the GoPro software. Since the GoPro can do shots for time-lapse, can the software assemble them into a movie file for you?
If you're on a Mac, there's a way to use QuickTime to create a movie from still frames, but I don't recall the specifics. Try googling.
Once you get your still series converted to some kind of movie format, there's a free program called MPEG Streamclip that runs on both Mac and Windows. It can convert just about any movie file to almost any other kind of movie file (but you might have to install other PAID software on your machine to convert to certain proprietary movie types). You can download it here:
http://www.squared5.com
I highly recommend MPEG Streamclip. It should be in every movie-maker's toolbox.
