Hello
Where do you check that shows 475GB? There can be hidden partitions reserved for system, firmware and whatnot, so if you look in File Explorere > This PC > C drive, you will see a smaller number.
If you right click on Start button and go to Disk Management, does it add up there?
As for TuboMode issue, I would suggest that you install latest BIOS from Acer's official website for your exact model and see if that helps.