iTunes 12.4, released earlier this week, has taken steps to simplify the user interface a bit. Although most of the same options are still there, they’ve been moved around and a few have been enhanced a bit in the process. View options have been taken out of the location on the top-right drop-down menu and have returned entirely to the traditional View overlay dialog found in pre-iTunes 12 versions — accessible using the Show View Options or by simply pressing CMD+J.
Although artwork sizes remain fixed in Grid views, you can use this dialog to resize the album artwork when viewing Artists, Albums, Songs, Movies, or TV Show episodes as a List view. To do this, bring up the View Options, ensure “View As” is to set to “List” and then use the “Artwork Size” slider that appears. Artists, Albums, and Genres in the Music section provide five different size options, while other list views such as Songs, Movies, and TV Show Episodes allow you to choose from three sizes.