Replacing artwork in iTunes

Is there a way to replace album artwork easily in iTunes?

My sizeable iTunes collection has become a bit unwieldy of late - and in my 'house-keeping' I find I have a lot of old, low quality album art I copied from the Internet and dragged to iTunes. It was better than nothing, but not by much.

Today, to replace album art I must go in to iTunes, click on the first individual song in an album, right click, click on "Get Info", click on "Artwork", click delete, click "Next", then repeat the process for every bloody song in the album. Once clear, I can ask iTunes to search for updated artwork, or if I must add it manually, copy and paste to the entire album.

It's long and tedious, and I usually give up after 2-3 albums. Is there a way for iTunes to do this for me? Is there at least a way to delete all the album artwork at once for a selected group of songs, so I can replace them?

Fred