To backup files, all you do is pretty much copy and paste files and folders and place them outside the Feralheart folder. For example just put the folders on your desktop. This is so when you re-install or redownload you don't lose any downloaded mods and additions you added to the game, along with your maps and presets.
I would recommend moving folders such as Terrains, my_presets, Presets, Textures, Objects, Items, Sky, and any other folders which have any added files or made objects/sky/weather/maps etc.
As for the files, I would move Items.cfg and the Emotes.cfg file which are found in your main Feralheart folder.
Once you've moved all the folders and files that you want then I would proceed with re-installing and re-download
