Bluetooth is hardware and, alas, you can't download hardware.
I didn't check if that laptop does come with bluetooth hardware or can be configured to do so. In that last case, I don't know if you ordered it. Only you know what you bought and why you bought this Acer model and not another model from another maker.
If it isn't present, you can buy a USB dongle that has it. It will come with the necessary drivers. Be sure it has Windows 7 drivers (models with only XP drivers might be cheaper but unusable for you).
Just a new lap top,Acer aspire 5742 running windows 7, but cant see any indication it has bluetooth on it, anyone know?, and if i havent got bluetooth can I download it from the net? bearind in mind I am a novice!!