I had the same question when I went to update to Gen 3 and asked it on the Habitat Talk forum. This is the answer I got from John with cuddeback.
"that feature is only available thru the app, and you would need an active cell home to make the change, you designate a specific camera to send all images in Higher res, otherwise they will send thumbnails, an option for you would be to buy a monthly plan for one month - make the settings or changes you want and then turn the plan off. There will be several settings and options that will only be available via the app and a cell connection. On top of that, currently the only series that will take the hi res the command, is the L series, the G and j will later but it's not live yet."
It was disappointing to learn. Seems like it would be an easy option to put on the camera itself. Hopefully they change it in the future.