not enough space to upgrade

[drupstone]

Who can help me out? I have a upgrade standing but not enough space, I did clean up with apt-get but that is not enough ,
now I get the advice to: /etc/initramfs-tools/initramfs.conf optie compress=xz but I do not know what to do with this message in order to make space

[Impavidus]

Maybe you just have to remove some old kernels. What do you get from these commands?
df -h
df -i
dpkg --list | grep linux-