I want to change the grid style

For the 2014 theme I think the only way you can set it up is to have 6 total posts. three top three below that.

If the styling of the 2014 grid isnt what you are looking for, you might want to find another plugin that suits your styling more than that of the 2014. Might be easier then venturing into the world of completely having to redesign the grid roster through php and CSS editing.

Just a thought.

Unless of course I misunderstood and you were just wondering how you can actually get the grid system to post like that then the solution is easy: just grab a page, set it to sticky (top right side of the edit window under posting style) and set the Tag to “featured”.