Start – Settings – Control Panel – Administrative Tools Computer Management
Under storage, choose Disk Management, then on the right side of the screen, right click on the device (usually a CD-Rom) and choose “Change Drive Letter and Paths”

Note: this option is not available for the harddrive, if there is only one partition on it.

Note: If you have programs installed that rely on being on a particular drive, you may need to reinstall them, or edit certain configuration files to make them work again after doing this.