Narrow Margins and Space for text/pictures on Mobile

Hello!

I hope I am wording this correctly…

On a mobile device, my text and pictures are unable to stretch wider to fit the screen because it seems that the margins of the theme block it.

For example, a paragraph of text reads very narrow on the phone. I would like the margins to be wider, so that the paragraph looks shorter and wider rather than long and narrow. I would also like my pictures to take a fuller portion of the screen. Right now, they are reduced in size because of the limits of the margin.

Hope this makes sense and thank you for your help.