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
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!
OK Folks I want to thank you all. I have now manged to get all the artwork correct. And I still cannot believe that I did not see the images box in goggle.
inwanw
inwanw: Glad it worked for you. My library is looking much better also thanks to the responses on this thread.
I know that this thread is almost dead but I have to add this information:

Originally after getting good advice herein on how to upgrade the iTunes artwork I went to work upgrading everything using Amazon Music. Then, as a back-up plan, I checked out seekacover.com. Well, let me tell you, the difference between Amazon and seekacover is like night and day. I just finished re-doing all of the artwork using click and drag from seekacover. Their stuff is first class quality.

Just wanted to share that with any readers that may still be checking in.
Best source for album artwork for me is: google images. Just type in a rough approximation of the album /artist name and search using google images. You'll get dozens of photos of the album cover in varying sizes and quality. I prefer to keep data size down by going for images about 300 x 300 but you can go higher resolution if you like.