I'm set with the migration of several Wordpress themes that use Bootstrap 2.3.2. The choice is to use 3.3.7.
First off, I checked that there are no custom div IDs or classes used in the theme.
I then replaced the 2.3.2 CSS/JS Bootstrap files with the 3.3.7 equivalent files.
The layout was a mess as a result. Images are no longer responsive, and there is obvious viewport overflow in different devices.