How to Delete all contents on USB drive including the protected hidden partition using windows 7 or 8 (I used this method to fix the size of usb drive on Fire TV)
Right click the my computer icon
Check the Disk name for your usb drive mine is Disc 1
Now open cmd as administrator (right click and run as administrator)
You should now see a list of the disks online.
Type select disk 1 or whatever your disk number is you want to delete.
Type list disk again just to make sure you have the right disk selected it should say *Disk 1 Online.
Type clear this will delete all partitions including hidden EFB partitions and everything else on the disk.
Go back to manage disk drives and enable/format the usb drive.
If your Fire tv shows usb drive a 197mb then it is looking at the hidden partition on your usb drive follow the above instructions to fix this