openssl req -new -newkey rsa:2048 -nodes -keyout yourdomain.key -out yourdomain.csr

http://support.godaddy.com/help/article/3601/generating-a-certificate-signing-request-nginx
http://support.godaddy.com/help/article/4976/rekeying-an-ssl-certificate

# Be sure to remember to chain them!
cat gd_bundle-g2-g1.crt >> yourdomain.crt

# Move 'em
sudo mv yourdomain.crt /etc/ssl/certs/yourdomain.crt
sudo mv yourdomain.key /etc/ssl/certs/yourdomain.key

# Now make sure everything is chained properly
http://www.sslshopper.com/ssl-checker.html