First, make sure your hardware has Windows 8 drivers. Then read this http://technet.microsoft.com/library/jj203353.aspx , it will explain how the upgrade works from Vista. Short version, you will need to re-install your programs and make sure you back up your data. As above, if you have a .edu emlai address (meaning that is a student upgrade price), you can get that version. You also can't upgrade directly from a 32 bit version to the 64 bit version so will need to do a full clean setup.
As another note, are you SURE you want Windows 8? Most people do not like the interface, you may want to look at Win 7 64 bit instead.