Following on from my post at http://www.forlinux.co.uk/expertise/blog/2011/11/10/how-to-generate-a-csr-for-an-ssl-certificate/ you can also generate a new CSR (Certificate Signing Request) without having to fill out all of the company details all over again.
To do this you will require the existing certificate (.crt file) and key (.key file), if the certificate is correctly installed on your server then you should be able to find the location of these from your Apache configuration file.
Once you have those you can run the following command to generate a brand new CSR, for your certificate renewal.
openssl x509 -x509toreq -in existing-certificate-name.crt -out signing-request.csr -signkey existing-key-name.key
This will then give you a file outputed of signing-request.csr which you can use to purchase your certificate from your preferred SSL vendor.