My mautic stopped working after host upgraded the server

I have old version 2.16.3 and it just stopped working
I could not login
My host apparently adopted 8.1 PHP…few days ago.
I put some code into htaccess to force php70 but still cron is not triggering…
Any idea?

Also can I upgrade my version directly by overwriting newer files and update db?

1.make a backup
2. Update to Mautic 3 via command line
3. Update to Mautic 4 via command line

HI Joey
Can you be more specific…
I would love to upgrade…
I need to download 2.6 version to my local dev and run it there…
can I update it with composer?
Or command line like GItbash? I am on PC, that is why it is confusing