Download the 64 bit file if you have a computer with 4 GB of RAM or more or if you plan to upgrade your RAM to 4 GB or superior. Next check how much memory your system has. It will only be different if you opted for a system with Windows 7 Professional or Windows 7 Ultimate.
iso file to pick from, look at the base of your system: It will most likely be Windows 7 Home Premium. iso files are the disc images digital river would send out to customers purchasing Windows 7 and have nothing else added. iso file if planning on switching from 32 bit Windows 7 to 64 bit Windows 7.
iso files are very large (~4 GB each) and require the use of high speed internet to download.
