[CentOS] yum update / kernal update failed - remove or repair

I have a VPS running C7. I ran a 'yum update' which included a kernel update. The yum update wasn't a total success because mariadb updates failed. However everything else appeared to work.

However, when I rebooted the server it did not restart. I have managed to get the ISP's support desk to boot the server by selecting the previous kernel, and I now have access to my box again.

As I will probably only have one chance to fix this (without having to get the ISP's help again) I was wondering if there are any clear instructions on how to remove a failed kernel RPM update, returning the server to the state it was in prior to the YUM update?