To safely remove the unwanted kernel, open a terminal session and run the command:
Find the kernel package name
dpkg -l | grep 3.19.0-31
On amd64/x86_64 it is linux-image-3.19.0-31-generic.
Remove (purge - remove all configuration files as well)
sudo apt-get purge linux-image-3.19.0-31-generic
