1. All the songs you buy via iTunes are now DRM free, so you can play them with every software and player you want.

2. The bitrate has now doubled, which results in much better soundquality for the music.

Luckily,  the iTunes store has a feature that will automatically (for a small fee) upgrade all  songs that you previously bought! You can find the feature if you go to ‘quick links’ on the right, and click on ‘Upgrade my Library’.

iTunes

iTunes will give you the option of deleting your old library or moving it to the desktop before replacing it with the new files.  The best option is to keep it, should  you ever need the lower quality 128 kbps songs, since the original downloaded ones will be better quality than if you have to re-compress the new 256kbps down to 128.