It's super simple.

Take out the black bezel by unscrewing the two screws on top then pulling it out forward. Then you'll see the main gauges, there should be a two screws on both sides and one on top. Once you unscrew those, pull out the entire guage and you'll notice three black knobs holding the green bulb that you can turn to remove the bulb. Take out the default green bulb and replace it with a red 194/168 bulb (LED's don't spread light as good but it's bright). Do the reverse to put everything back together and you're done!