to renew a cert just do as root
:move or remove: /etc/httpd/conf/httpd.pem

cd /etc/pki/tls/certs
Look in the Makefile file for the number of days you want the cert for. (change it to your taste)
Check the first line of the Makefile and set the serial number you want.
make httpd.pem
respond to the questions
cp httpd.pem to /etc/httpd/conf/httpd.pem

and restart httpd service.

This should do it.