dondestroyonload problem

Actually I want to make a high score board.
I used the playerprefs and set it is DonDestroyOnLoad
but the problem is after I finish the game, then the game will go to the scoreboard scene. If I press replay, I will go back to the game scene. Now the playerprefs is still here right. After I finish the game again and go to scoreboard scene. It will spawn one more playerprefs in my game. As a many time of this actions. Now the game have a lot of playerprefs now. So how can I destroy the past of them and keep the update version of playerpref?

Actually I want to know how to script dun create another one when I still have the old one.

Also I want to keep the most update one of the PlayerPrefs that with a update score in it.

Sorry for my confusing question, may be I’m so tired yesterday.