Hi, after you changed the kernel to 4.4, you need to change your network interface name in /etc/network/interface as the kernel change eth0 to something like ens3 (like my case - confirm it with ip addr show)
Then restart networking service you should be fine :)

Your best option at this point would be to port your applications to a new server running Ubuntu 16.04. This will ultimately save you time, and be the most surefire way to get up and running on the latest kernel.

Droplets originally based on 14.04 still use our older kernel model where the kernel is managed outside of the Droplets themselves. This article explains how this works and shows how to update your kernel:

• How To Update a DigitalOcean Server’s Kernel

The key is to make sure the version in the panel and the Droplet match. You can check the kernels available to your Droplet by running:

ls /boot/vmlinuz*

So if you selected “Ubuntu-16.04 kernel-4.4.0-21” in the control panel, you’ll need to have this in the output:

/boot/vmlinuz-4.4.0-21-generic

If you’re still running into issues, please go ahead and open a support ticket so the team can take a closer look.

Note: For Droplets based on 16.04, the kernels no longer need to be managed through the control panel. So depending on your use case, it might just be better to move to a new Droplet rather than update in place.