The ONLY way to switch from 32-bit to 64-bit is to install Windows 64-bit from scratch via clean install ... there is no upgrade path from 32-bit to 64-bit.
I have a Dell Inspiron 1545 laptop purchased in march of 2009.  I've put 4 GB or ram and replaced the HHD with a 250 GB Samsung Evo.  I just upgraded the system from 7 to 8.1 and have been trying to figure out how to get the thing on the 64 bit system.  Microsoft was little help saying that they were not sure but believed that I would have to change the motherboard and everything in order to run at 64 bit.  then they suggest that I go to Dell for help.  I just want this thing to run as fast as possible.  my computer properties say this, "32-bit Operating System, x64-based processor".  Can and how do I get this thing running on 64 bit so it will run as fast as possible?
going from windows 8.1 32 bit to 8.1 64 bit