Kernel installation requires restart?

Hi

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After installing a new kernel do i have to restart the server?

Code:

Installing : kernel-2.6.32-504.3.3.el6.x86_64

Also do i have to add again all kernel optimizations on sysctl.conf?

Thanks

 

If i install a new kernel using yum update and i don't reboot and then after a few days i install again using yum update a newer kernel and then i reboot it will auto load the latest one?

Thanks