Why would you use a separate plugin to change a font?
You should add the font directly in your theme’s header and adjust the CSS accordingly.
For example, using Roboto from google fonts – https://fonts.google.com/?selection.family=Roboto:
In your theme’s header.php add this line before </head>:
<link href="https://fonts.googleapis.com/css?family=Roboto" rel="stylesheet">
In your theme’s style.css add the font to your elements, as needed – for example:
body {
font-family: 'Roboto', sans-serif;
}
If you need more help understanding how this works, I think this resource could be a good place to start: https://developers.google.com/fonts/docs/getting_started