I get the below error when I try to install updates using Software Updater: Not enough free disk space The upgrade needs a total of 81.3 M free space on disk '/boot'. Please free at least an additional 15.9 M of disk space on '/boot'. Empty your trash and remove temporary packages of former installations using 'sudo apt-get clean'. What should I do? firmtechnologies@FirmTechnologies:~$ (ls -l /boot) total 155801 -rw-r--r-- 1 root root 1158016 May 3 01:30 abi-3.13.0-24-generic -rw-r--r-- 1 root root 1161713 May 8 01:31 abi-3.13.0-26-generic -rw-r--r-- 1 root root 1161713 May 15 20:07 abi-3.13.0-27-generic -rw-r--r-- 1 root root 1161764 Jun 4 22:57 abi-3.13.0-29-generic -rw-r--r-- 1 root root 165510 May 3 01:30 config-3.13.0-24-generic -rw-r--r-- 1 root root 165538 May 8 01:31 config-3.13.0-26-generic -rw-r--r-- 1 root root 165521 May 15 20:07 config-3.13.0-27-generic -rw-r--r-- 1 root root 165544 Jun 4 22:57 config-3.13.0-29-generic drwxr-xr-x 5 root root 1024 Jun 6 14:31 grub -rw-r--r-- 1 root root 29091568 May 7 21:31 initrd.img-3.13.0-24-generic -rw-r--r-- 1 root root 29094684 May 12 12:24 initrd.img-3.13.0-26-generic -rw-r--r-- 1 root root 29095678 May 18 10:57 initrd.img-3.13.0-27-generic -rw-r--r-- 1 root root 29093700 Jun 6 14:32 initrd.img-3.13.0-29-generic drwx------ 2 root root 12288 Apr 30 17:11 lost+found -rw-r--r-- 1 root root 176500 Mar 12 13:31 memtest86+.bin -rw-r--r-- 1 root root 178176 Mar 12 13:31 memtest86+.elf -rw-r--r-- 1 root root 178680 Mar 12 13:31 memtest86+_multiboot.bin -rw------- 1 root root 3372643 May 3 01:30 System.map-3.13.0-24-generic -rw------- 1 root root 3377429 May 8 01:31 System.map-3.13.0-26-generic -rw------- 1 root root 3377429 May 15 20:07 System.map-3.13.0-27-generic -rw------- 1 root root 3378267 Jun 4 22:57 System.map-3.13.0-29-generic -rw------- 1 root root 5776416 May 3 01:30 vmlinuz-3.13.0-24-generic -rw------- 1 root root 5790912 May 8 01:30 vmlinuz-3.13.0-26-generic -rw------- 1 root root 5790912 May 15 20:07 vmlinuz-3.13.0-27-generic -rw------- 1 root root 5792544 Jun 4 22:57 vmlinuz-3.13.0-29-generic