The upgrade needs a total of 81.5 M free space on disk '/boot'. Please free at least an additional 17.4 M of disk space on '/boot'. Empty your trash and remove temporary packages of former installations using 'sudo apt-get clean'.
http://askubuntu.com/questions/142926/cant-upgrade-due-to-low-disk-space-on-boot
Run below command as suggested in the error message.
$ sudo apt-get clean
First check your current kernel version.