Apple Cider Vinegar is pretty acidic so it would increase the acidity in your body instead of reducing the acidity in your body.
Still your body has ways of keeping the acidity in your body at correct levels so even though the Apple Cider Vinegar may increase acidity in your body it won't increase it by much.
Also some people have reported that Apple Cider Vinegar does become Alkaline so it may reduce acidity in your body but there's no guarantee.
Eating leafy green vegetables and drinking some Alkaline based water can help reduce the acidity in your body.