How to change album artwork for an album with multiple songs on Itunes?

[Lakers2k10]

The album I have on iTunes is not in the store so it cannot get the album artwork for it, but I've noticed that all the albums that have multiple songs for them cannot have their artwork changed, just their info which is absolutely dumb. In Zune software all I have to do is change the image simply by right clicking it but anyway, how can I change the artwork for an album with multiple songs?

For example, I am trying to change the album artwork for the Motion Picture Soundtrack "Friday" and it has multiple songs in the album but this complicated iTunes software will not let me change the album artwork so its just shown as a Generic Album.

Someone help me.