How to change font ?

it looks like you already added in place for your headers, but to do it sitewide you’ll need to look for this –

body {
	background: #f2f2f2;
	color: #333;
	font-family: 'Open Sans',"Helvetica Neue", Helvetica, Arial, sans-serif;
	font-size: 18px;
	font-size: 1.125rem;
	font-weight: 300;
	line-height: 1.625;
}

Then you’ll need to follow whatever tutorial they have to setup the font with the theme. Just do a search for whoever you’re getting the font from (whoever is hosting it).