I just picked one up myself an have been looking into the same thing myself. Here’s a few links and a youtube video I found that show how to do it. I haven’t tried it myself yet so I can’t give you my word on it, but they all seem to say about the same things as how to do so I’d trust them:
You don’t “adjust the velocity” of an airsoft gun.
You can adjust the hop-up, though, if that’s what you mean.
As far as muzzle velocity goes, use a stronger or weaker gas.
I can’t help you as far as adjusting the hop-up goes, sorry, I don’t own the gun and am not aware of where the unit is accessible.
I just picked one up myself an have been looking into the same thing myself. Here’s a few links and a youtube video I found that show how to do it. I haven’t tried it myself yet so I can’t give you my word on it, but they all seem to say about the same things as how to do so I’d trust them:
https://www.airsoftcanada.com/showthread.php?t=13768
http://www.youtube.com/watch?v=GD9g5UnU2qk