I've seen a few requests in here to upgrade from Font Awesome 4 to 5. Unfortunately v5 was not backwards compatible with v4, and it was a tough upgrade to make.
However, now that v6 is out, I thought it might be worth posting again. I haven't tried it, but apparently they learnt their lesson and v6 is backwards compatible with v4.
If you’ve been with Font Awesome for a while, you may have noticed that upgrading to version 5 was a bumpy ride for many, and we learned a lot along the way. To ensure a smoother upgrade experience, we doubled down on testing and squashed every bug in sight.
We tested many upgrading-to-v6 scenarios and tweaked our docs accordingly. That means Font Awesome 6 is backward compatible, and upgrading should be straightforward, even directly from version 4. Old icon names, old unicode values trapped in CSS pseudo-elements, or icon styles (e.g. ‘fa’) don’t break when switching to v6.