You can control all the Presets via the template manager configuration. All 6 presets appear at Extensions → Template Manager → rt_reaction_j15 → Presets.
You would then adjust the parameters in Settings to meet your requirements. On selection of a preset, the administrator automatically updates the Settings to match that particular preset. This is where you will edit the options to meet your requirements such as CSS Style. This system allows you to quickly and effortlessly customise a preset to your liking.
The options are as follows, and the areas that they control are indicative in their name:-
In the event that you need to customise all the preset arrays, and do not wish to use the template administrator, then you can customise the preset arrays in the gantry.config.php file. Do note that it is much easier to use the template administrator, and editing the preset array is only really necessary if you wanted to use multiple custom configurations on your site which is uncommon.