Well, it has been pasteurized, so it has no yeast to do the work.
You will need to do the following:
1. Find some suitable wine yeast. Cote de Blanc or Pasteur Champagne works well. Try to avoid using bread yeast.
2. Take the lid off and replace it with a balloon. Put a pin-hole in the balloon (this is so your bottle doesn't explode).
3. Ferment it where the temperature stays around 55-65 F. Let it sit until it is fairly clear, and the junk has settled to the bottom of the bottle.
4. Add sugar or nutri-sweet if it tastes too dry for you.
5. This should result to something closer to wine than pruno.