how-do-i-make-hydrochloric-acid-more-concentrated
It depends upon how concentrated it is initially. Boiling away so-called excess H2O probably won't work because HCl forms a constant boiling mixture at about 22% HCl. I'm at a slight disadvantage since I don't know all of the details of what you are trying to do but there are two ways that come to mind. Both take a little doing.
1. Generate HCl gas (you can use H2SO4 and NaCl) and bubble the gas into the solution you have to increased the HCl content. There is a limit to how much HCl will dissolve.
2. Add concentrated HCl. Concentrated HCl is sold commercially as 12 M which is about the limit. 12M HCl contains approximately 36-38% HCl.