How to know which system I need 32bit or 64bit windows?

If your RAM is more than 4GB, so you have to install 64 bit window and 7f your RAM is kess than 4GB you can install 32 bit window.Although you can install 64 bit window on less than 4GB RAM but it will work slow and hangs  alot

if you RAM Memory bigger than 4GB, so you have to install Windows 64bit and if your RAM Memory less than 4GB you can install windows 32bit or 64bit