Hi Ricky,
I am not with Laminar Research; just a flight simmer from downunder on the other side of the world to greengolfer15.
A few additional comments.
The short answer to your question is yes download as many times as you like or want onto as many computers as you have and you don't have to pay for the download. BUT, if you run more than one copy at the same time then you will require additional licences (ie purchases). Why?
To run a digital download version you have to be connected to the internet at all times and the software does some silent checking while you are using X-Plane to confirm that you are running a legal copy of the software. If it detects that two or more versions are running using the same product key then "watch out".
If you have already downloaded X-Plane I would strongly suggest you copy the downloaded installed product to another location on your PC as a backup. If you still have the zipped files then copy them as well or as an alternative.
If you suspect you have a problem with the installed software you can solve the problem by running the installer program again. While it is running it will detect any files that are corrupted and or insert any files that are missing. This avoids any full uninstall and reinstall process. If and when there is an update you will be asked if you want to update in the first instance. If you say yes then this is what happens when you perform an update.
Welcome to X-plane.
Glenn