Apple is now allowing iTunes Store customers to upgrade previously-purchased DRM-encoded tracks to the higher-quality, DRM-free iTunes Plus format on a track-by-track basis. Up until now, users were forced to upgrade on an all-or-nothing basis, angering some users with larger iTunes Store-purchased music libraries, who were faced with upgrade costs in the hundreds, or even thousands, of dollars. U.S.-based users may upgrade individual songs for $0.30…
