In order to do this you need to go to what is called the Disk Management Console which is located in Computer Management Console. The easiest way to do this is to:
1. Go to My Computer icon on your desktop.
2. Right click it and then select Manage.
3. This will open up the Computer Management Console. If you expand the Storage Group you will find Disk Management.
4. Click Disk Management and you will find all your physical drives listed.
5. Select the drive where you want to change the letter, right click it and select Change drive letters and paths.
6. Follow the wizard to change the drive letter of your disk.