If you already have the software, why "download" it again? Downloading is copying something from the internet to your hard disk.
I don't know the program, so I can't tell you if it has an option to specify the storage location for its data. If it has, most likely you tell it that it should be a folder on an external hard drive. Check the manual or the help, or look around in the menu.
But it's a bad idea to 'store' data on an external drive. This forum is full of posts by people who found there external drive failing for some unknown reason. External drives are much more error prone than internal drives, and slower moreover. Why do you want it? What's wrong with your internal hard disk?
Whereever you store it, be sure to regularly make a good backup. That's required with an external hard disk (because it's so unreliable) and highly recommended with an internal one (because those fail also).
Kees
I have Quickbooks Premier 2004. Can I download the software on a desktop and save all data on an external hard drive instead of saving info on the desktop?

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