As per my knowledge, you need to delete the upgraded kernel manually and its entry in grub.conf file. Just try the below step.
1. Once we upgraded our kernel our old kernel will not be deleted , check inside /boot you can see two kernels.
2.Just boot by your old kernel and delete the new upgraded kernel manually.
3.Then delete the new initrd.img file.
4.Delete the new kernel's entry in /etc/grub.conf file.
5.Reboot your machine.
Note: Don't fear no data will get loss.