[OS X TeX] Updating packages

[Theo Moore]

Hi,

I'm a bit puzzled when it comes to playing around with tex packages
and distributions. A while ago, I installed the MacTeX-2009
Distribution. However, one of the packages I use (pgfplots) has some
very recent updates (late 2009 and early 2010) that I need.

Can someone please hand-hold me through the process of updating the
pgfplots package?

Thanks!