delete old kernels

List the kernels installed:

jay@pilsner-xubuntu:~$ dpkg --list | grep linux-image-[0-9]
rc linux-image-3.5.0-17-generic 3.5.0-17.28 i386
rc linux-image-3.5.0-27-generic 3.5.0-27.46 i386
rc linux-image-3.5.0-28-generic 3.5.0-28.48 i386
rc linux-image-3.5.0-30-generic 3.5.0-30.51 i386
. 
.
.
ii linux-image-3.8.0-34-generic 3.8.0-34.49 i386
ii linux-image-3.8.0-35-generic 3.8.0-35.50 i386 
 
jay@pilsner-xubuntu:~$ sudo apt-get autoremove
Reading package lists... Done
Building dependency tree      
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

So I deleted all the "3.5" kernels:

jay@pilsner-xubuntu:~$ sudo apt-get --purge autoremove linux-image-3.5.0
jay@pilsner-xubuntu:~$ sudo apt-get autoclean