Using twenty-ten; want to go responsive: How?

Well, I’ve searched for three hours here and the Net, and I’m still lost.

I have a site on WAMP localhost—not live—using a twenty-ten child theme that I was about to put up live.

I want the site to be “responsive,” and so far, I’ve been told to use a current responsive theme instead of a responsive plugin.

I’ve altered the css in the twenty-ten child theme dramatically to change the layout, colors, etc. of the site—looks nothing like the original twenty-ten.

Can someone please tell me the best and least problematic way to change to something like the twenty-fifteen theme and still maintain the look of the present site? Keep in mind: It’s on a WAMP localhost install.

I thought about starting from scratch with twenty-fifteen, but MY LORDY!, what a lot of work! I thought I’d ask all of your brilliant minds what’s a Hobbit like myself to do in this situation before I do something that will come back to haunt me.

Any help with this will be much appreciated.

Is there a way to insert a jpg screenshot image into a post?