"Agera One" is correct - but may have misinterpreted your question.
YES.. you can change to a 64 bit OS.. your specs are fine and can run a 64 bit version of windows just fine..
(and you will benefit with being able use all your RAM).
But you cant use a windows upgrade process for the move..you will need to do a clean install of windows 64 bit.
and unless you have a retail version of windows that contains both 32 and 64 bits options.. you will need a new licence.
Hope that clarifies.
Cheers