I was susprised to see they didn't have instructions too. Here you go:
Download the free app sysex librarian, install it on your computer. Launch the app, and drag the new OS sysex file into it. Make sure the midi connection in the app is set to Pro3 (which needs to be connected via USB to your computer first). Then press play and wait while it transfers. After it transfers, the OS will still need to go through an automatic saving procedure and a warning will show on the display saying NOT to turn off the Pro 3. Once that is done, you will be prompted to power cycle the Pro3 to complete the update. When it boots back on, go into the (new) Global menu and select Reset Globals to complete the process.