Color Problem Recognized. Assistance Required.

Much as I love the idiosyncratic way that our American cousins treat the English language, I’m getting a bit annoyed with all the words that get highlighted in red because of apparent misspelling when I’m typing something in Word. I know there’s probably an easy way to change the underlying language rules to avoid things being changed to humor, center, favorite, etc. (plus a whole of bunch of other words that seem to require a ‘z’) but I just can’t be bothered digging around to find out how to do it. Any helpful advice would be much appreciated.