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
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.
I search for the image I want, then download it into My Pictures first. I have Google Toolbar installed with the Picture widget, cycling through My Pictures. So I get a random slide show of all the covers I have downloaded - kind of cool.

After that, it's pretty much what's posted above. I use Download from iTunes first, as it's the fastest way and the image is not stored inside the file. But in many cases, iTunes does not give me the Cover I want. So I have to replace it.

There are three different ways to get the artwork in there. Choose the one you like.

Just be sure it's applied to all tracks - not just the first one of the album. Highlight the track and ensure a picture displays on lower left - use the down arrow to work through all the tracks and check.

Regards,
OK,
Going to just tag this on as I am trying to find all the album covers. Best sites to get artwork from? Would love to hear where everybody get artwork from. Or how they use goggle for this, never done it that way

Inwanw
Inwanw,

To google artwork:

Open browser, type google.com in address field, click "images" link at top left corner, type in album title in search field, click "search images" button, select the image that matches your album and looks best to you.
Thanks to all for the instruction: It works! Inwanw: I use two sources for the artwork: Amazon Music and seekacover.com. Both seem to have good quality stuff. If I'm not totally happy with one image I switch to the other site for comparison. That's it though, I'm not one to roam all over the place. Again, thanks to each of you.

As a side note, last night after getting the advice from Sidssp I started working up the updates and 10 albums into the project the darn wireless router went out on me. I'm just now (1:00 PM) the next day getting back into it. Aarrggghh!