If I were you I would reinstall windows and do the 64bit version. Your Windows key will work with either 32bit or 64bit version. And yes 32bit will only see 3.25GB of ram cause the x86 architecture which is 32bit. That goes for all operating systems that are 32bit. Once you go to 64bit you can use a lot more ram and that would then depend on your motherboard supporting it. Most high end motherboards support 32GB of ram or more now these days.
What will happen if you stay with 32bit is the other 4 and 1/2 gigs of ram would be useless and you won't have no performance gain compared to 64bit.