---GRUB and Kernel---

uname -a ##show current kernel, hostname, time, etc

yum list kernel ##show kernels installed

yum remove kernel-3.10.0-229.11.1.el7.x86_64 ##this will uninstall this kernel, make sure when you uninstall a kernel it's not the one currently running the computer, use 'uname -a' to show current kernel

/boot/efi/EFI/centos/grub.cfg ##show grub bootloader config for UEFI BIOS, cat this file to see the current boot options, if this does not exist see grub2/grub.cfg below

/boot/grub2/grub.cfg ##bootloader config for BIOS, cat this file to see the current boot options

/etc/grub.d/40_custom ##edit this file to add custom boot entries, paste contents from grub.cfg starting at 'menuentry 'CentOS Linux 7...', then edit 'CentOS Linux 7...' and give it a custom name, also edit boot options or kernel

grub2-mkconfig -o /boot/efi/EFI/redhat/grub.cfg ##after editing '40_custom' run this command to rubuild grub