You can not do an in place upgrade to 64bit from 32bit, it must be a clean install. But yes you can use an upgrade disk to do a clean install, that is format the drive and install windows 7 fresh.
64bit will allow full use of 4gb's of ram, you will notice only about 3.2 gb's show up under 32bit windows, keep in mind that my computer properties will show 4gb's is installed, but its not all usable by the system.
Is it worth it? A better question would be why not? Check all devices for 64bit drivers. Only thing I ran into not working was one of those usb to serial cables. Everything else worked great, been using 64bit windows for a few years now.