I have updated the kernel on my Red Hat Enterprise Linux Server release 6.7 (Santiago) from 2.6.32-573.22.1.el6.x86_64 to 2.6.32-642.1.1.el6.x86_64 and as per Red Hat documentation https://access.redhat.com/articles/3078 kernel version 2.6.32-642 will update the release to RHEL 6.8. However if you look below it still shows as 6.7 (Santiago). I am not sure why the difference ? I have also rebooted the server after the kernel was updated.
[root@test-dev-001-par user1]# uname -a
Linux test-dev-001-par user1.hello.world.net 2.6.32-642.1.1.el6.x86_64 #1 SMP Fri May 6 14:54:05 EDT 2016 x86_64 x86_64 x86_64 GNU/Linux
[root@test-dev-001-par user1]# uptime
16:02:35 up 5:16, 1 user, load average: 0.43, 0.34, 0.33
[root@test-dev-001-par user1]# cat /etc/redhat-release
Red Hat Enterprise Linux Server release 6.7 (Santiago)
[root@test-dev-001-par user1]# cat /etc/issue
Red Hat Enterprise Linux Server release 6.7 (Santiago)
Kernel \r on an \m