Removing Green and Blue Color Bars And Top Blog title

Is there a way to eliminate the color blocks that show up in the theme on the sidebars as well as eliminate the middle white section that has the blog title between those two color blocks? I would love to just have a header color and then the blog right below without blocks of color on the side bars. And since I’m removing the blocks of color, I want to remove the white Blog Title section in between them so the body is one perfect rectangle. Thank you!