the cpu is 64-bit. you're mixing up the cpu with the operating system. your operating system is 32-bit which is not the same thing at all. they do not mean the same thing for the system. it's perfectly normal to have a 32-bit windows with a 64-bit processor. we had 64-bit processors long before 64-bit windows became the norm. 64-bit windows was needed to address larger amounts of ram (over 3.5 gb) and a few other things that slowly became the norm for pc's. but again, 32 bit windows on a 64-bit cpu is perfectly normal and nothing to worry about.
any reason you want to upgrade to 64-bit windows other than thinking you need it with the 64-bit cpu? otherwise if everything works fine and you have less than 4 gb of ram, then it really is...