Upgrading 32 Bit OS to 64 Bit OS

I was a windows 8 64-bit user before. I downgraded my OS to 32-bit as what was required by my work programs. Now that I already have a laptop intended for my work loads, I want to upgrade the OS of my previous laptop back to 64 bit. Is it possible? If it is, how should I do it?

Thank you in advance for your response. :)