How do you get your downloaded version of simcity 4 deluxe from your old computer to your new computer?

It all depends on what you actually downloaded, from where, and whether or not you saved that download. If the download was a legitimate purchase, then you should be able to re-download it from the same site you bought it from at no extra cost (check your account with the download provider). If you cannot re-download it, the only way to effect the transfer is to locate the download on the old computer, and copy it across using removable media (flash drive, writeable DVD, etc) or by networking the two computers together.

If you didn't save the download (you ran it instead) and you cannot re-download it, then you'll have no option but to purchase it all over again. If you're lucky, you might find a copy of the download in your internet cache but if too much time has passed then it's unlikely to still be there.

Note that some downloads are often supplied as a "stub" installer. These are small EXE files that, when run, download the actual installation files and then perform the install. These are best avoided, especially if your Internet connection is slow. Standalone installers are better as you only need to download the installer once -- provided you save the download. Never run a download without saving it first, especially if it is a large download.