sudo apt-get

to get the latest updates

sudo apt-get update

sudo apt-get upgrade

to clean up left-overs

to upgrade your operating system to the current version

via GUI

sudo apt-get update

sudo apt-get upgrade

gksudo "update-manager -c"

from CD

sudo mount -o loop ubuntu-9.04-alternate-i386.iso /media/cdrom0/

gksu "sh /cdrom/cdromupgrade"

via CLI

sudo apt-get update

sudo apt-get upgrade

sudo apt-get dist-upgrade

what version am I running?

$ cat /etc/issue

Ubuntu 8.04.2

$ cat /proc/version

Linux version 2.6.24-22-generic (buildd@vernadsky) (gcc version 4.2.3 (Ubuntu 4.2.3-2ubuntu7))

$ cat /etc/lsb-release

DISTRIB_ID=Ubuntu

DISTRIB_RELEASE=8.04

DISTRIB_CODENAME=hardy

DISTRIB_DESCRIPTION="Ubuntu 8.04.2"

$ uname -a

Linux ubuntuhost 2.6.24-22-generic #1 SMP Mon Nov 24 18:32:42 UTC 2008 i686 GNU/Linux

$ uname -r

2.6.24-22-generic