Share 'Adjusting Tension on a Banjo Head'

Being relatively new to minstrel banjo, I was wondering how to go about adjusting the tension on a banjo head.  Mine seems to be rather flexible and lately I have noticed a buzzing when playing.  I am guessing this has to do with the humidity and the head needs to be adjusted once in a while to compensate.  How do you know for sure the head needs to be adjusted and how do you tell when the tensio…