If your bow has room to tighten the limb bolts,find the proper size allen wrench and turn each limb bolt the same amount until you get the bow where you want it poundage wise.
That is true as long as your tiller is set correctly to begin with.
As far as adding performance, I'm not sure what you mean. It will increase your bows energy, but you will probably have to re-tune your setup and may even have to change the spine of your arrow. Will you notice the increased energy - probably.