Recharging AC

[RedRocket]

We have just had our 04 Vibe for about 3 months and when we got it,we didn't check the AC,it was 20 degrees out..LOL But we turned it on and noticed that it isn't very cool..When you turn the AC button on,the compressor (ac unit) clutch kicks on,but it just doesn't get real cool..Im thinking it needs recharged..I never have recharged one before,is there a certain amount that it should have? How do I figure out how many pounds it has in the system and how many more it needs?