How much RAM max for MBP C2D 2.4 GHZ


I have a unibody MBP 2.4GHZ( 2009 ) that I am trying to decide if I should upgrade to a newer machine or upgrade RAM etc...

This machine is 2.4Ghz and has 4GB RAM in it.
I was wondering if I could upgrade this machine to 8GB or 6GB.
Any ideas?