Need a computer guru to explain the 32 vs. 64 bit scheme?

Have an old EMachine (T3612) that had Windows Vista Basic with an upgrade to Home Premium. Later downloaded Widows 7. You will quickly learn that I am not computer literate. The Windows 7 was 32 bit. I learned some time after that the original setup was a 64 bit. It had 512 memory and we added 512 more. I need to understand how this impacts on the computer's performance, if at all. The Motherboard is a Coconut Creek, Chipset is Intel, Modem is Conexant, Lan is Intel, and Audio is Realtek. The computer is old, but operates fairly well (reliant). Updating all of the program data resulted in a layering of updates that I am hesitant to eliminate without knowing which is the latest and correct program. Can anyone out there help me understand what may have happened in the change from 64 to 32 bit and how to eliminate the excess programatic downloads?