Renew certificate SSL

I take over the management of the Pydio site and I have to renew the certificate. It is a certificate from a certified authority, therefore not self-signed.
I did some research but I could not find anything convincing. If anyone has a procedure / site or any other track to help me.
Plateform Linux Ubuntu 13.04


basically if you are using apache you just need to replace the .key and .crt files with the new, or atleast put each in the same folder and then go to your pydio’s virtual host file and put the new certificates.