I am new to SSL certificates. At work we have just renewed one of our SSL certificate. Basically we used the key (whatever.csr) that was already used for last renewal and we got the new certificate sent. Now I guess the only thing that I need to do is cp the certificate to the expected path (the one specified in httpd.conf) to replace the old one...right?
Basically my old certificate expires on the 18th. I have copied the
new certificate to the expected directory then I have changed the
CertificateFile directive to point to the new certificate. When I
SIGHUP'd Apache everything worked yet I the certificate that I could see from my browser while visiting the site showed that it still expired on the 18th. I'm puzzled?

Was I suppose to create a new key? or was it ok to use the same key originally used last year? I mean it's only a signature...

CSRs don't have the expiration date in them. You typically can use the same one, as long as you haven't changed your private key.

If you have openssl, try this:

openssl x509 -in httpsd.pem -text

where httpsd.pem is the name of your actual certificate.

That will verify the expiration date. Also, make sure you're changing the correct entry in your httpd.conf file and that you have actually restarted apache.