Feral Heart itself is a pretty big game. Plus the additional downloaded Maps/Mass Masking/and Items. If you perhaps need to clear up some more space, then perhaps you should remove some programs you don't use that often. Or perhaps you should clean out your Internet browser and throw away some old homework files you don't need anymore. I'm sure the amount if probably 1GB, but I'm not compleat lay sure on how big the game is exact.
Try going into, "Start" and then "Control Panel", then after that click on Remove or add Programes and you can perhaps make room be uninstalling a few things.