Hi RockRanger3,
Thanks for visiting Apple Support Communities.
See this article for the steps to download a previous purchase:
Downloading past purchases from the App Store, iBookstore, and iTunes Store
http://support.apple.com/kb/HT2519
You may also want to enable automatic downloads for future purchases by using the steps in this article:
iTunes Store: How to enable Automatic Downloads
http://support.apple.com/kb/HT4539
Regards,
Jeremy