If you do everything properly then yes there is no risk. So once again please follow this advise:
First of all you would need to back up your website just to make sure you prevent loosing any of your content. You would need to open the Theme Options in a separate tab in your browser and keep in open. Then go to appearance, select default theme and delete smartIT theme, Then install updated theme theme. Once you done with that go back to that tab with the Theme Options and click there Save all changes, by doing it this way none of the customization added through Theme Options would be lost.
We are really sorry for delayed reply. You can check the theme version you are using by opening the theme thumbnail in the Appearance> Themes and compare to the version we have posted on the themeforest. We have made this update year ago and as far as I remember we haven’t minify css and JS scripts. Yes the previous version might have some issues with 4.3.1.