Hi Pattychow! Welcome to the website!
Why do you want to go to 32-bit if your system is capable of running 64-bit?
Nearly all 32-bit software will run on the x64 Windows 7 OS. Plus if you have 4GB of RAM or more it will fully utilize that hardware and your system will be quicker too.
If you still want to go to the 32-bit Windows 7 then you'll have to do a "clean" or custom install. In addition, you'll have to either delete the partitions and make new ones or reformat them prior to install.
However, why downgrade to 32-bit? The 64-bit operating system is here and now. Nearly all CPUs and hardware are for 64-bit. Windows 8, more than likely, will not even be offered in a 32-bit version.
Regardless, it's your decision however you want to setup and run your computer system.