How to convert windows 7 64 bit to 32 bit
As already said, you will have to re-install Windows. First make sure you have your Licence Key, if it's not on a sticker on your machine, use Belarc Advisor software from herehttp://www.belarc.com/free_download.html
Then, if you don't have a Win7 installation disk you can legally downlaod a copy of Windows from herehttp://forum.notebookreview.com/windows-os-software/428068-legal-windows-7-download-links-just-like-vista-before.html
Choose 32bit version, download as an iso and burn it to a disk
Back up any personal data, set your machine to boot from your new disk, and when the option becomes available during setup, do a fresh install. Download drivers from your machine's manufacturer and install.