I think you can upgrade by downloading the combo update and running it, That's the way I did it.

I think you may need to mess up with EFI Strings, but I'm not sure as I never got HDMI working myself either.

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My Hardware
CPU: Intel Celeron G530
Memory: 4.00 GB DDR3 1333Mhz
Graphics: NVIDIA GeForce GTX 550 Ti
OS: Mac OS X Lion 10.7.4 - Vanilla kernel
Motherboard: Gigabyte GA-H61M-D2-B3