I'm new to Ubuntu and I'm getting an error in software updater. When I try and do my daily updates, it says:

The upgrade needs a total of 25.3 M free space on disk /boot. Please free at least an additional 25.3 M of disk space on /boot. Empty your trash and remove temporary packages of former installations using sudo apt-get clean.

I tried typing in sudo apt-get clean into the terminal but I still get the message. All of the pages I read seem to be for experianced Ubuntuers. Any help would be appreciated. I'm running Ubuntu 12.10. I want to upgrade to 13.04 but understand I have to finish these first.

EDIT: @Alaa, This is the output from typing in cat /etc/fstab into the terminal:

# /etc/fstab: static file system information.
#
# Use 'blkid' to print the universally unique identifier for a
# device; this may be used with UUID= as a more robust way to name devices
# that works even if disks are added and removed. See fstab(5).
#
# <file system> <mount point>   <type>  <options>       <dump>  <pass>
/dev/mapper/ubuntu-root /               ext4    errors=remount-ro 0       1
# /boot was on /dev/sda1 during installation
UUID=fa55c082-112d-4b10-bcf3-e7ffec6cebbc /boot           ext2    defaults        0       2
/dev/mapper/ubuntu-swap_1 none            swap    sw              0       0
/dev/fd0        /media/floppy0  auto    rw,user,noauto,exec,utf8 0       0
matty@matty-G41M-ES2L:~$ 

df -h:

Filesystem               Size  Used Avail Use% Mounted on
/dev/mapper/ubuntu-root  915G   27G  842G   4% /
udev                     984M  4.0K  984M   1% /dev
tmpfs                    397M  1.1M  396M   1% /run
none                     5.0M     0  5.0M   0% /run/lock
none                     992M  1.8M  990M   1% /run/shm
none                     100M   52K  100M   1% /run/user
/dev/sda1                228M  222M     0 100% /boot
matty@matty-G41M-ES2L:~$ 

dpkg -l | grep linux-image:

ii linux-image-3.5.0-17-generic 3.5.0-17.28 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-18-generic 3.5.0-18.29 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-19-generic 3.5.0-19.30 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-21-generic 3.5.0-21.32 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-22-generic 3.5.0-22.34 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-23-generic 3.5.0-23.35 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-24-generic 3.5.0-24.37 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-25-generic 3.5.0-25.39 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
ii linux-image-3.5.0-26-generic 3.5.0-26.42 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP
iF linux-image-3.5.0-28-generic 3.5.0-28.48 i386 Linux kernel image for version 3.5.0 on 32 bit x86 SMP