Hi amslyn23,
Welcome to Apple Support Communities.
It sounds like you want to download a past purchase on your computer but aren't seeing the option. This might happen if you're using more than one Apple ID or the file is already in your iTunes library. Take a look at the article linked below for more information and the steps for downloading past purchases.
Download past purchases
http://support.apple.com/kb/ht2519
Download previous purchases on Mac or PC
- iTunes 10.3 or later
You need iTunes 10.6 or later to download previously purchased movies and TV shows.
- iTunes account in a country where iTunes in the Cloud is available
iTunes Store
Open iTunes and go to the iTunes Store.
Click Purchased in the Quick Links section.
Select the content type that you want to download (Music, Movies, TV Shows, Apps, or Books).
Select Not in My Library to view purchased content that isn't on your computer.
- Find the item that you want to download. You can browse using the menu to the left. If you have more than 2,000 songs, you will see Recent Purchases instead of All Songs or Albums.
- Click the Download icon next to the item you want to download.
If an item is already in your library, the Download icon won't appear.
Cheers!
-Jason