Go to https://store.djtechtools.com and got to "Account & Help" at the top right of the screen, and sign in. If you are logged in already it will say "Welcome (Your Name)"
Go My Account, then to "Order History"
Click on your order and you will see all the information. Print the page, and save it as a PDF. Or you can take a screenshot.
If your order is older than October 2012 then you will need to contact support to get your receipt.