You can reset your downloads by following these steps:
1. Logging In to your Account Page
2. Click on Itemized Order History
3. Scroll down until you see the items you wish to download and click the Reset Button to the right of the Item Name
Your downloads will be reset shortly. You are allowed 3 resets per product per 3 month period, if you exceed this limit you will recieve a "Download attempts exceeded" error.
At this time, there is no available feature that will allow you to reset your entire purchase history.