Changing from Windows 7 32-bit to 64-bit...?

I'm stuck in a situation right now. I have a Windows 7 OS 32-bit, but I'm thinking about upgrading it to a 64-bit now since i have more RAM. I know that people have asked so many times, but do I really have to reformat my hard disk in order to change the OS in the process? Its the same OS cept i'm just changing 32 to 64 bit. I have over 180gb of information but i dont have an external hard drive to back it up. So is clean installation the only way?