Microsoft windows setup assign drive letters to hard disk partitions itself, but sometimes it become necessary to customize the drive letters according to your needs, following is the procedure to change the drive letters:

• Right-click ‘My Computer’ icon and click on manage.
• Go to ‘Disk Management’

• Right-click the drive and click on ‘Change drive letter and paths’

• Click ‘Change’, a dialog box will appear asking you the drive letter you want to assign to that partition, select the drive letter you want to assign to that drive, it would not allow you to change the drive letter of your boot partition.
• Click Ok, and yes and then click Ok, Now the drive letter has been changed.