Upgrading iTunes Artwork


I want to upgrade the quality of some of the cd artwork in my iTunes library but I cannot delete the old artwork without deleting all of the music tracks as well. How do I delete the existing artwork (not the music) so I can import (click and drag) better quality artwork in.
puerto
Very simply. If the old artwork was downloaded by iTunes, select the tracks, control click (or right click for Windows) to bring up menu, select Clear Downloaded Artwork menu item.

If the old artwork was user added, select the tracks, control click (or right click for Windows) to bring up menu, select Get Info menu item.

In the dialog, if you had selected multiple tracks, you will see an Artwork box on the Info page. Simply drag the new graphic file onto that box to replace the artwork.

If you had selected only a single track, you will not see an Artwork box but you will see an Artwork tag instead. Click that tag and delete the old artwork there.
Sidssp: Thank you! I just now did "upgrade" one bit of artwork but am struggling with the second one. . it just doesn't want to change! I'll get it - you have me on the right track!! I'm following your input on the other thread as well. Your explanation is good - I'll respond over there as it develops. Thanks again.
Sidssp: OK! I got it - your advice was perfect. Now I will be up all night upgrading iTunes artwork - your fault!
in iTunes I select all the songs on the album needing a new or different artwork. I highlight the artwork window. Then I open my web browser, go to google images and search for the cover I need. I search for the best, then I copy the image to the clip board. I return to iTune. I paste it into the artwork frame I had previously highlighted. I can't paste the picture with the mouse but I can with edit command menu. I had to learn this because iTune doesn't like some of my older MFSL cd's or it just can't located any artwork.