Hey nancy solomon!
If you have songs that you have purchased in the past that are DRM protected, then the best way to upgrade those files will be to subscribe to iTunes Match:
iTunes Store: iTunes Plus Frequently Asked Questions (FAQ)
http://support.apple.com/kb/HT1711
Can I upgrade my previously purchased music to iTunes Plus?
Yes. If you subscribe to iTunes Match, you can download your previously purchased music again in the iTunes Plus format. To do so:
- You need to delete the original DRM song from your library first. Doing this enables you to download the song again in the iTunes Plus format from iTunes in the Cloud.
- Click the Purchased tab in the iTunes Store.
- Click Music.
- Locate the artist of the song you want to upgrade.
- Click the iCloud Download icon next to the song you want to upgrade.
Thanks for being a part of the Apple Support Communities!
Regards,
Braden