change playerpref number by one

hi. what do I have to do to add 1 to a playerpref value? I'm using it to count the number of deaths and save it for next time the player plays the game.

here's my code

 function OnTriggerEnter (other : Collider)
 {
  if (other.CompareTag ("Enemy"))  //if the player hit's the enemy
     {
      PlayerPrefs.SetInt("Player Deaths", 1);  //set player deaths to +1
      yield WaitForSeconds(0.05); // wait some time
  Application.LoadLevel(Application.loadedLevel); //reset the scene
  print (PlayerPrefs.GetInt("Player Deaths"));  //print "Player Deaths"
     }

I tried writing this:

 PlayerPrefs.SetInt("Player Deaths", +=1);

but it just gave me an error

• Assets/Scripts/Controlls.js(91,45): BCE0043: Unexpected token: +=.