Hi and welcome!
You should save the installation file you download in a safe place for future re installations (on your hard disc, an external HD, USB memory, DVD-R...).
If everything goes wrong, i bet you can contact AGEOD and they will provide another download link, but this is not the standard way.
AGEOD doesn't have a permanent redownload system like Steam and the like.
I use to store the file and the key in a couple of HD just to be sure

.