Windows 7 Windows 7 32 bit. on computer now. Want 64bit. no option for 64bit. on windows 7 upgrade disk. Why?

Hello, my windows 7 became corrupted, so reinstalled from upgrade disk. Had windows Vista on my Toshiba Satellite A505-S6960. when new, the computer came with a upgrade that was sent to me. I reinstalled windows 7 because of problems with my external WIFI adapter was not installing after a windows up date. I did not see a option for the 64bit. operating system on the auto run disk for windows 7 upgrade. I want to know how I can get the 64bit version back on my computer at this point.