Or you can change it without having to buy software.
I'm just going to assume you use Windows XP/2K (if not, you need to rethink what you're doing ).
Right click My Computer -> Manage, click on Disk Management. Now you should see your drives and such. Right click the drive you want to change the letter and path of, and give it a new path.
Alternatively, you can go into Control Panel -> Administrative Tools -> Computer Management. Click on Disk Management, and same thing as above.