Threat to creativity

Hello , I am using the Threat To Creativity theme and I wonder if it’s possible to make the main page only have one row of posts at left going down instead of three rows of posts from left to right. (sorry my bad english)

I mean :

|post box|
|post box|
|post box|
|post box|
|post box| etc..

Instead of :

|post box| post box| post box|
|post box| post box| post box|
|post box| etc..

Thanks for help!