How do I change to the new Kernel version

How do I change to the new Kernel version

How do I change to the new Kernel version
Need to update the system. first check current version of kernel
use sudo uname -r command.
Open the terminal and run sudo apt update for Ubuntu.
if system is CentOS/RedHat/oracle Linux box then, first clean cache.
run sudo yum clean all.
now run yum update.
once system upgraded after that system need to reboot.
some time after reboot system new kernel version not coming. in this condition
need to check grub.conf file. what is default value.
#boot=/dev/sda
default=0
timeout=5

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