If you need to modify grub at boot:
One option is to edit grub before selecting an image and changing your boot option to default to terminal session instead of a graphical load. the steps can be found here How do I boot into single-user mode from GRUB?. I know the answer for Ubuntu but it also works on CentOS, I have had to do this before.
If you are stuck at a graphical loading page:
If your system gets stuck trying to load a graphical interface, try and just do a CTRL+ALT F2
(RHEL based systems) and get into a terminal session.
Once your in a terminal session:
Once you are signed into the terminal session, you can just yum history
to pull up your install history and reverse your installs.
RedHat gives out a really good explanation on how to use yum history
to rollback installs
How to use yum history to roll back an update in Red Hat Enterprise Linux 6 , 7
Here is a Note for the yum history rollback from the given link.
Note: Rollback of selinux, selinux-policy-*, kernel, glibc (dependencies of glibc such as gcc) packages to older version is not supported. Thus, downgrading a system to minor version (ex: RHEL6.1 to RHEL6.0) is not recommended as this might leave the system in undesired state. Use the yum history option for small update rollbacks.