CiviHosting provides two options for SSL certificates, free “Let’s Encrypt” certificates and paid-for “RapidSSL” certificates.
Let’s Encrypt is a certificate authority that provides free SSL certificates, accepted by most browsers. While they provide security and authenticity when accessing your site over SSL, they do not provide end-user warranties or the additional features of commercial certificates.
For a Let’s Encrypt SSL certificate, just login to your hosting Control Panel and click on the SSL tab and then follow the procedure there.
A RapidSSL (commercial certificate) is what you have purchased previously and you can renew yours here: