It is pretty easy to change the default font family for Bootstrap. You just need to add a few lines of CSS to your stylesheet.
Here is an example of how you can change the font family to "Open Sans":
@import url('https://fonts.googleapis.com/css?family=Open+Sans');
body {
font-family: 'Open Sans', sans-serif;
}
You can find more information about how to use Google fonts with Bootstrap here:
https://getbootstrap.com/docs/3.3/customize/#web-fonts
