If you want to take up the waist a bit, it is an easy hand tailoring job. However it can be confusing because you're working on the outer edges of the aprons, where things overlap. To make it an inch smaller, you'd think logically "I'll take up a half inch on each side." You'd be wrong! You need a full inch on each side.

Good info here on how to do it.

On the left side, move the strap. On the SWK Economy, it's sewed onto the under-apron at the hem. Move it back from the edge by whatever distance you need. I would put a small piece of fabric on the underside to reinforce the apron material. You don't need to re-hem the edge, just let it overlap under the button-hole when you slip the strap through.

On the right side, move the top buckle. I agree with McMurdo that you should try leaving the lower buckle where it is---see what happens. See the link above for hints from a professional.