When you receive the following message on terminal:
The following packages have been kept back:
0 upgraded, 0 newly installed, 0 to remove and 6 not upgraded.
Execute the following command to upgrade your kernel to latest distribution
sudo apt-get dist-upgrade
You will no longer get the message “The following packages have been kep back:”
Run the following command to free up some space occupied by your old kernel images
sudo apt-get autoremove
Answer Y to free up space
After this operation, 270 MB disk space will be freed.
Do you want to continue? [Y/n] Y