If you no longer need an SSL certificate on some domain and would like to use it for your future projects/other active domains, you can uninstall the certificate.
For this, just open SSL → Manage:
And click on the options button (⋮) → Uninstall:
If it is a Lifetime SSL from Hostinger, after uninstalling the certificate it will appear in the SSL section of your panel for future use.
After the SSL certificate is uninstalled, your website will only be accessible by HTTP. Trying to load it as HTTPS will show error
If you would like to temporarily disable HTTPS to have your website available by HTTP, you can unforce HTTPS