Meanwhile, the performance of the box will be improved a lot after the upgrade.
Step 1 :
sudo apt-get update
Step 2 :
sudo apt-get install linux-generic-lts-xenial linux-headers-generic-lts-xenial linux-image-generic-lts-xenial linux-tools-generic-lts-xenial
Step 3 :
sudo apt-get remove linux-image-generic-lts-utopic linux-headers-generic-lts-utopic linux-image-generic-lts-vivid linux-headers-generic-lts-vivid
Step 4 :
sudo apt-get autoremove
sudo apt-get autoclean
Step 5 :
sudo update-grub
Step 6 :
Reboot your box.
REMARK
If you are running Croissants (IPS) on Ubuntu 14.04 LTS, you can upgrade the Kernel to 4.4.0 as well. You just follow the captioned steps.
That's all! See you.