Download certbot at https://certbot.eff.org/lets-encrypt/pip-other.
Stop Apache.
Run certbot-auto like this:
$ chmod +x certbot-auto
$ sudo ./certbot-auto renew -force-renewal --dry-run --preferred-challenges http
If this does not produce any error, you can rerun it without the --dry-run option:
$ chmod +x certbot-auto
$ sudo ./certbot-auto renew -force-renewal --preferred-challenges http
Restart Apache.