Other than baseball caps, most hats don't offer much in the way of size adjustment. However, you can easily tighten just about any hat with a strip of elastic and some thread.
Snapguide user J. Angel suggests sewing a small strip of elastic from some old (clean) underwear to the fabric ring inside the hat. The resulting bridge will shrink the hat to your specifications and add a little flexibility if others want to borrow it.
You will need some very low-level sewing skills to attach the elastic, but the whole process shouldn't take more than 10 minutes.
Make Your Hat Fit Tighter [Snapguide]