Different kernels in same Xubuntu (16.04.3)

[MR ZenWiz]

I'm running Xubuntu 16.04.3 on my desktop and my laptop.

The desktop was installed from a fresh 16.04.1 image and has been kept
up to date.

The laptop was installed form a 16.04.2 DVD and has been kept up to date.

However, my desktop is running (now) the 4.4.0-91 kernel, and my
laptop is running the 4.10.<something> kernel.

Why would that be?  How do I get the desktop up on the 4.10 kernel
(safely) without a reinstall?

Thanks.
MR