Figured it out for a Mac:
1.Connect the phone to iTunes.
2. Hold down the Option button and press "Check for Update."
3. Browse to the ISPW file that you want to upload.
4. Wait for the upgrade magic to happen!

__________________
Jeff
Current:
'07 Jeep Wrangler
'06 BMW X5 3.0i

Former:
'12 WRX; '08 WRX; '06 BMW X5 4.8is Dinan S1; '02 BMW 530i Dinan S2