What do you exactly mean? Normally deaths etc. are not counted by minecraft. Only modifications like plugins or the scoreboard do that? What do you want to reset?
The Plugin that I use is called "ScoreBoardStats" and I think it is the only one of statistics that is in Aternos, I would like to restart the statistics without needing to delete the Plugin, as I had done before.
I think it is enough to delete the folder of the plugin and not the plugin (.jar) itself. After that you can restart the server and the folder will be automatically recreated.