As the other replies to this state, yes it's standard practise to update a kernel by installing the newer one without having to re-install or update all the other packages. Kernel updates are handled the same as any other package update but with the only difference being that a system reboot is required. (There's also the possibility of performing live kernel patching so that a reboot isn't needed, but that's typically a paid for service with enterprise linux).
Also, you can have many kernels installed concurrently and select which one to boot from at the GRUB boot screen. This is mostly used when you update the kernel and suddenly find on rebooting that something has gone wrong (e.g. necessary drivers not included in the initial ram disk - initrd), so you can reboot and select the previous working kernel to boot the system and resolve whatever issue you had.
Also, you can have many kernels installed concurrently and select which one to boot from at the GRUB boot screen. This is mostly used when you update the kernel and suddenly find on rebooting that something has gone wrong (e.g. necessary drivers not included in the initial ram disk - initrd), so you can reboot and select the previous working kernel to boot the system and resolve whatever issue you had.