If you want to change the letters assigned to your fixed or removable drives:
Right Click on My Computer
Select Manage
Select Disk Management
For a Fixed Disk:
Select it
Right click
Select Change Drive Letter and Path
Click on the Edit button
Enter in the letter you want to use
For a Removable Disk:
In the lower, right hand panel, right click on the Disk or CD ROM #
Select Change Drive Letter and Path
Click on the Edit button
Enter in the letter you want to use