How to adjust my epson HC8350 gamma?

At the risk of sounding unhelpful, I would take note of the default values, tweak one of the values a few notches and then rerun the sweep and see how the gamma had changed at that particular ire. This should help you figure out which way you need to go.

In its simplest term, higher light output would mean a lower gamma value; and vice versa. So if a mesurement point has a measured gamma value lower than your target (meaning you need to raise your gamma), you will need to lower the light output. That's it.

The challenge here is that you need to figure out, for your particular Epson's projector model, what each point corresponds to what input level (or levels). It may be as simple as the leftmost point corresponds to 10% input level; the second leftmost point corresponds to 20% level, and then 30%, 40%, etc. But it may be not as straightforward as that - meaning one point may affect a range of input levels (say the rightmost point may affect 70% - 90% levels - just for example). You need to try that out by yourselves.

The following link may help:
http://www.avsforum.com/t/1134710/epson-calibration-guide-1080-1080ub-6100-6500ub-7500ub#post_16166537