javascript - FontAwesome Update - Old Icons to New

I have a large website that uses FontAwesome. Recently we upgraded from 4.6 I believe to the latest version.

After the upgrade all of our icons are broken. A lot of the far/fa not working but if I change them to fa-solid they work.

The issue is the site is incredibly large with a lot of files so it can multiple days going through all these files to correct the icons.

Has anyone got a quicker solution for this to make the latest font awesome work?

Icons are broken after an update to the latest version.

Solution:

Yogi's comment of backwards compatibility saved me. Thanks bro