When you download something and it is saved on psp common how do you get to it?

You will want to take the Memory card out of your PSP and plug it in to your computer if your computer can read the card, If not then you will have to plug it in to a card reader for your computer. Now to get to the common Folder follow these steps:

My Computer> Click on your memory card> Find and Open the PSP Folder> Then Open the Common Folder.

Hope I helped