Consolidating all iTunes music files to one location

I have many music files, purchased from the iTunes store and downloaded from my own CDs, stored on my C drive. They are organized into many iTunes Playlists, which are very important to me.

I have 2 Local User Accounts on my PC (don't know why, I wish it were just one).

In iTunes, I can see the file location for each song...both user accounts are being used.

I would like iTunes to see all of my music files stored under the same local user...let's call it User #1.

How can I move the files showing a location in iTunes under User#2 to User#1?

Of course, I want to do this in a batch, not one song at a time.

And of course, I will back up all my music files to my external drive.

Also, do I have to do something with my iTunes Music Library file as well?

Please advise--thanks.