[CentOS] update to 7.4

I was doing an update to 7.4 and somewhere in middle the machine died.

If I drop back to a previous kernel the machine is alive. So how do I say
"forget the previous yum update" and start all over and do it again.

Booting into the new kernel I get a kernel fault. So going back one level
on teh boot screen solves that - I just need to start the update again. How
is that?

Thanks,

Jerry