If your boot partition is getting full and your running the machine as a server and have no GUI you can run this command to remove all those unecessary kernel images if you update frequently they can take up quite a bit of space.

dpkg --get-selections|grep 'linux-image*'|awk '{print $1}'|egrep -v "linux-image-$(uname -r)|linux-image-generic" |while read n;do apt-get -y remove $n;done

You may also need to update GRUB  /usr/sbin/update-grub after this has completed.