Change a partition letter without disk management

The easy way is to open Disk Management (diskmgmt.msc) and right click and chose change partition letter. But for ex in windows embedded posready 2009 you do not have this option.

Open regedit and navigate to HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices
Rename \DosDevices\D: to \DosDevices\E:  for ex and then restart windows.