Question regarding upgrading OS/files

Hey guys, I'm currently using a 32-bit Windows 7 computer, and I want to upgrade to a 64-bit version of Windows 7. I'm running an Athlon II x4 processor, so I know that it's capable of it. I also only have 4 GB of RAM installed, but I want to be able to use all of it, instead of just 3.1 GB. Is it possible to do this and keep all of my files/programs on the same drive? If so, how could I?

Thank you!