On the hosting dashboard of your website you should be able to renew your SSL certificate. With 1and1 for example they allow you to renew the certificate up to 6 times a year.
If in doubt talk to your web designer or your hosting company support.
The new version of Chrome released in January no longer supports SSL certificates issued by Symantec or any companies owned by them (Thawte, Verisign, Equifax, GeoTrust and RapidSSL) if issued before 1st June 2016.
If you have a security certificate and your site has been HTTPS for a couple of years you will be wanting to renew the certificate. Why? Well, if a user happens to be using the latest Chrome to view your site they will get a warning which looks something like this.
This could put the user off, and worse still there is an option to report your site to Google which could affect your ranking in search engines.