SSH to your instance and switch to ghost's user.
Then following these commands:
1. Install latest ghost-cli
sudo npm i -g ghost-cli@latest
2. Renew certificate
ghost setup ssl-renew
3. Switch to root user
sudo su
4. Upgrade acme.sh inside letsencrypt
"/etc/letsencrypt"/acme.sh --upgrade --home "/etc/letsencrypt"
5. Renew SSL through acme.sh
"/etc/letsencrypt"/acme.sh --cron --home "/etc/letsencrypt" --debug --log
Reload browser, Tada!