How can I untag wrong album artwork in itunes?

Hello all,

I was wondering if anyone can tell me how to untag wrong album artwork in itunes. I am able to add new artwork to albums in which itunes could not find the art work by "get info" for song and then find it out on the internet. However, when I find artwork for wrongly tagged artwork and I go to "get info", delete wrongly tagged artwork, and then try to add the correct artwork, the original wrongly tagged artwork remains. Do I need to restart itunes each time?

Thanks in advance,

Jim