If you ordered it as a download then you might find a download link available in your Adobe account online. You can also download CS5 applications thru the following page:
CS5 - http://helpx.adobe.com/creative-suite/kb/cs5-product-downloads.html
Since it is an upgrade you will need to have the serial numbers from the purchase and from the version you upgraded from. These should be available thru your Adobe account online.