You want to set the drive letter of a volume.
Using a graphical user interface
Using a command-line interface
The diskpart command lets you assign drive letters from the command line. First, start by running the command in interactive mode:
List the current volumes on the system:
DISKPART> list vol
From the output, select the volume in which you want to set the driver letter. In the following command, we're selecting volume 0:
DISKPART> select vol 0
Now, assign the drive letter you want. In the following example, we're assigning letter F:
DISKPART> assign letter=F
When volumes are made active and removable media added to a system, they are automatically assigned the next available drive letter (in alphabetical order starting from C). It is a straightforward operation to change the drive letter of a drive, but you need to be sure nothing references the prior drive letter. If you attempt to assign a different drive letter to an existing drive that is currently in use, the system will let you do it and allow both the old drive letter and new drive letter to be used until the system is rebooted. After the system restarts, the old drive letter will go back into the pool of available drive letters.
MS KB 234048, "How Windows 2000 Assigns, Reserves, and Stores Drive Letters," and MS KB 223188, "How To Restore the System/Boot Drive Letter in Windows"