Change OS system drive letter

it is by rating the tip below.

Many things can contribute to your system drive making itself a letter other than "C" (during install), such as other partitions on the disk, commercial utility partitions or Citrix changing your path to "M" (they give you this option while installing).

Go into Disk management and try to change the system letter - NOPE, sorry. So you're stuck unless you reinstall, right? Wrong!

To change the drive letter of your system partition, open regedit and navigate to hive:

HKEY_LOCAL_MACHINESYSTEMMountedDevices

Here you will see a key for each of your drive letters on this system, prefixed by "DosDevices" and followed by the drive letter of that device ("DosDevicesC:").

To change your drive letter say, from an "F" to a "C", locate the "DosDevicesF:", right click, rename and change the "F:" to a "C:". (Note: make sure that there isn't a C already. If there is, change THAT to something else FIRST using the same technique).