Responsive DIY Template Default for v1.5.x

[hols.club]

I have upgraded successfully to Zencart v1.5.5 but was interested in changing my Abbington Mega site into a responsive one

Therefore my question is after reading the FAQ's I still wasn't sure.
To transform my site to either the included responsive classic or The Westminster New, Winchester Black, Winchester Responsive, and Responsive Sheffield Blue v2.0 do I:
1. Install a responsive plugin
2. Compare files between a new template and abbington mega (I use winmerge) and add all the differences into the new template files
3. Then select new template on admin

or
Is there a more elegant method to merge files for a new template?

[ideasgirl]

How can you manage that on your demo the 3 columns of centerboxes go down to 1? Mine are only decreasing in size but continue being 3. I haven't found where to change those parameters. If I change them in admin, then it will change it to desktop, which is not what is wanted.