Need help about changing the main keyword of a niche site

Hello guys, I tried to find my answers on the google and here but without any success, so I'm asking you a few questions.

I have a niche site that is about 6months old and I targeted a kw that has about 250 monthly local searches and niche is ranked #1 - #3 on google for that kw. This page is making a few bucks here and there. I found a better related keyword that has around 1.5k mothly searches and few other keywords that has about 1000 searches each. What do you think of changing the complete structure of the page? A new menu, a new homepage and new kw that I target? Is it a smart move? How would that affect SEO of the page?

P.S. I targeted that kw because I didn't have a clue what I was doing.

Thank you in advance. Best regards.

why not making a new page for the new KW ???
or target the new kw with a new subpage where you use the kw as name and put some links there.

i mean www.yourdomain.com/newkeyword

Thank you for your suggestion. What about homepage? Set a homepage with this new keyword?