If you are just trying to raise the abv, you can simply up the base malt (as it does not contribute as much to color or flavor) or add some extra light malt extract. You may have to adjust the mash temperature to keep the body where you want it. In my opinion you should not really need to mess with the specialty grains or hops as that will affect color/flavor/bitterness where you just seem to want more boozy bang for your buck. You can boost the abv some by adding corn sugar but I really would not put more than 10% of the fermentables as simple sugars as that can cause a cidery flavor. be sure to alter your pitch rates accordingly though, you do not want to stress your yeast.