If they are already installed then adjusting them is easy, however on some cars they gain absolutely zero power. Some they do though so maybe you'll be lucky. Back to adjusting them : There should be four small nuts around the edge of each gear (3 if you got the shitty AEM ones) surrounding one larger center nut. First loosen all the outer nuts a couple turns, dont remove them. Now take a wrench or socket to the larger center nut, I wanna say 12mm, and slowly turn it to the right or left depending on if you wanna retard or advance that particular gear. There will be marks on the gear representing how many degrees of timing you are advancing or retarding. Once the gear is where you want it, tighten the 4 smaller surrounding nuts. I would only recommend doing this if you have some dyno time on your hands, you will never notice the difference on the street. Also, I tried numerous different configurations when messing with mine and found the best to be zero'd on both gears. If you do see any gains, I would expect no more than 10whp. Good luck.
You would be more likely to gain torque from the exhaust gear than HP from the intake gear. Some people have reported 15 RWTQ with the exhaust gear alone. I ran it alone for about a year before finally getting the intake gear, haven't redynoed yet but I doubt it gave much at all. Oh well, at least it looks better now.