Check Which Kernel is Currently in Use
To display both the kernel version and your system’s architecture (32-bit or 64-bit), type:
uname -ir
Upgrading All Packages and Using the Newest Kernel
sudo apt-get update
sudo apt-get dist-upgrade
sudo reboot
sudo apt-get install update-manager-core
sudo do-release-upgrade
Reference
How To Upgrade to Ubuntu 16.04 LTS | DigitalOcean How To Update a DigitalOcean Server’s Kernel | DigitalOcean