In short, you can't change it.
'Member' - is because you aren't a Full Member (that's a member who paid a subscription).
'Active member' - is related to the amount of posts you made on the forum. The more posts you got - the higher you get (native, tenderfoot, bushcrafter, etc.).
Andy beat me to it ...
I agree with Andy regarding making a sticky thread with this sort of info, I'll be happy enough to write one somewhere next week after my exams have ended