You can use a recipe calculator to determine how much DME to add, just enter all the ingredients then you can play around with the additional amount to get the ABV you're looking for. Brewer's Friend has an easy to use, free recipe calculator. I strongly recommend more DME vs. sugar, but a combo would be good. Another way to up the ABV and add a flavorful adjunct is my favorite - Agave. Fermentable, clean, and adds some body.