Apple is changing the way iTunes users can replace their existing iTunes songs to the new DRM-free versions. Initially, the only option available was to convert every iTunes-purchased file to the new sans-Fairplay version, for 30 cents a track, using the “Upgrade My Library” feature.
Today, Apple has switched to a per track and/or per album model whereby users can chose which songs in their library they want to convert to DRM free versions. The iTunes store is not yet 100% stocked with DRM-free versions of songs, as it will take until April for it to fully ingest the new content.