1. if you are happy with the currently kernel in Ubuntu 16.04, then you can stay with this kernel (it's version 4.4) and it gets supported until 2021).
2. if you want to jump to the new supported and tested (tested in 16.10) 4.8 Linux kernel, then there is a command described in https://wiki.ubuntu.com/Kernel/LTSEnablementStack that helps you upgrade.
However, when you upgrade the kernel (and Xserver stack that are linked together), your Linux kernel will be upgraded every six months from now on, until 2021. The next kernel version update will be in July, and it will be whatever Linux kernel was released in Ubuntu 17.04.
In a nutshell,
1. if you are happy with the currently kernel in Ubuntu 16.04, then you can stay with this kernel (it's version 4.4) and it gets supported until 2021).
2. if you want to jump to the new supported and tested (tested in 16.10) 4.8 Linux kernel, then there is a command described in https://wiki.ubuntu.com/Kernel/LTSEnablementStack that helps you upgrade. However, when you upgrade the kernel (and Xserver stack that are linked together), your Linux kernel will be upgraded every six months from now on, until 2021. The next kernel version update will be in July, and it will be whatever Linux kernel was released in Ubuntu 17.04.