To accomplish this, you will want to follow these steps:
In Joomla navigate to Administrator → Extensions → Templates Manager and select the template you are currently using as your default.
Navigate to the Fonts settings tab.
Select Yes in Use Google Font if you want to use google fonts. Otherwise select No.
If you select Yes in Use Google Font on Google Font Family add the font you want. To get Google fonts names click in this link.
- If you select No in Use Google Font in Font Family select any template fonts from the dropdown.
Add the Font size you want in px.
- Do the same for the Menu and the rest as h1, h2 etc .
- After finishing this Click Save button
Your site will get the Fonts you selected.