A clean install is required, which means you have to re-install all installed programs and backup and restore any data. Other then the 64bit version requiring additional memory and the need for for device drivers that may not be available in the 64 bit version you should keep the 64 bit version. If you have a separate drive partition you may want to install the 32 bit verison as a dual boot, if you have enough disk space available. You also have the option os installing XP mode with the Professional version of Windows 7.