nicomachus@nicomachus-Inspiron-N5110:~$ ls -lh /boot
total 110M
-rw-r--r-- 1 root root 1.2M Jun 17 20:03 abi-3.13.0-55-generic
-rw-r--r-- 1 root root 1.2M Jun 19 05:04 abi-3.13.0-57-generic
-rw-r--r-- 1 root root 162K Jun 17 20:03 config-3.13.0-55-generic
-rw-r--r-- 1 root root 162K Jun 19 05:04 config-3.13.0-57-generic
drwxr-xr-x 5 root root  12K Jul 11 15:54 grub
-rw-r--r-- 1 root root  11M Jul  7 21:37 initrd.img-3.13.0-54-generic.old-dkms
-rw-r--r-- 1 root root  27M Jul  4 13:37 initrd.img-3.13.0-55-generic
-rw-r--r-- 1 root root  27M Jul  4 13:37 initrd.img-3.13.0-55-generic.old-dkms
-rw-r--r-- 1 root root  27M Jul  6 18:28 initrd.img-3.13.0-57-generic
-rw-r--r-- 1 root root 173K Mar 12  2014 memtest86+.bin
-rw-r--r-- 1 root root 174K Mar 12  2014 memtest86+.elf
-rw-r--r-- 1 root root 175K Mar 12  2014 memtest86+_multiboot.bin
-rw------- 1 root root 3.3M Jun 17 20:03 System.map-3.13.0-55-generic
-rw------- 1 root root 3.3M Jun 19 05:04 System.map-3.13.0-57-generic
-rw------- 1 root root 5.6M Jun 17 20:03 vmlinuz-3.13.0-55-generic
-rw------- 1 root root 5.6M Jun 19 05:04 vmlinuz-3.13.0-57-generic
nicomachus@nicomachus-Inspiron-N5110:~$ sudo apt-get purge linux-image-3.13.0-54[sudo] password for nicomachus: 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'linux-image-3.13.0-54-generic' for regex 'linux-image-3.13.0-54'
Note, selecting 'linux-image-3.13.0-54-lowlatency' for regex 'linux-image-3.13.0-54'
Package 'linux-image-3.13.0-54-generic' is not installed, so not removed
Package 'linux-image-3.13.0-54-lowlatency' is not installed, so not removed
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
nicomachus@nicomachus-Inspiron-N5110:~$ sudo apt-get purge initrd.img-3.13.0-54-generic.old-dkms
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package initrd.img-3.13.0-54-generic.old-dkms
E: Couldn't find any package by regex 'initrd.img-3.13.0-54-generic.old-dkms'