Boiling vinegar will not concentrate it, since the acetic acid will boil away as well as the water due to it forming an azeotrope with the water. You will get a very little bit of concentration, perhaps. To effectively concentrate it, you have to do fractional distillation. You can find out how to do this on the web by looking up "fractional distillation" in google. By far the easier thing to do is just buy glacial acetic acid from a chemical supply house. Be careful with it, however.