So, I have a 32GB Samsung Galaxy J7 model J700H. I have used only 2GB of space including all my apps and misc files, but, in the storage tab, in Settings, it shows I only have 400mb, of space left when I should have 30GB left. Furthermore, if I try to install an app from Google Play Store, it warns me it is not possible due to the lack of space. But if I install the same app through an APK file, it works. In the Storage Analyzer app, it says that 30GB is used by Android, but the ROM itself can't possibly be that big. How can I free up this space?