First login to your Ubuntu system as any user with 'sudo' privileges and execute "sudo apt-get update" at the shell prompt. The output on your screen should appear similar to the following.

$ sudo apt-get update
[sudo] password for sudouser:
Hit http://us.archive.ubuntu.com jaunty Release.gpg                           
Ign http://us.archive.ubuntu.com jaunty/main Translation-en_US                
Ign http://us.archive.ubuntu.com jaunty/restricted Translation-en_US          
Hit http://security.ubuntu.com jaunty-security Release.gpg                    
Ign http://security.ubuntu.com jaunty-security/main Translation-en_US
Ign http://security.ubuntu.com jaunty-security/restricted Translation-en_US
Ign http://us.archive.ubuntu.com jaunty/universe Translation-en_US
Ign http://us.archive.ubuntu.com jaunty/multiverse Translation-en_US
Hit http://us.archive.ubuntu.com jaunty-updates Release.gpg
Ign http://us.archive.ubuntu.com jaunty-updates/main Translation-en_US
Ign http://us.archive.ubuntu.com jaunty-updates/restricted Translation-en_US
Ign http://us.archive.ubuntu.com jaunty-updates/universe Translation-en_US
Ign http://us.archive.ubuntu.com jaunty-updates/multiverse Translation-en_US
Hit http://us.archive.ubuntu.com jaunty Release
Ign http://security.ubuntu.com jaunty-security/universe Translation-en_US
Ign http://security.ubuntu.com jaunty-security/multiverse Translation-en_US
Hit http://security.ubuntu.com jaunty-security Release
Hit http://us.archive.ubuntu.com jaunty-updates Release
Hit http://security.ubuntu.com jaunty-security/main Packages       
Hit http://us.archive.ubuntu.com jaunty/main Packages
Hit http://us.archive.ubuntu.com jaunty/restricted Packages
Hit http://us.archive.ubuntu.com jaunty/main Sources
Hit http://us.archive.ubuntu.com jaunty/restricted Sources
Hit http://us.archive.ubuntu.com jaunty/universe Packages
Hit http://security.ubuntu.com jaunty-security/restricted Packages
Hit http://security.ubuntu.com jaunty-security/main Sources
Hit http://security.ubuntu.com jaunty-security/restricted Sources
Hit http://security.ubuntu.com jaunty-security/universe Packages
Hit http://us.archive.ubuntu.com jaunty/universe Sources
Hit http://us.archive.ubuntu.com jaunty/multiverse Packages
Hit http://us.archive.ubuntu.com jaunty/multiverse Sources
Hit http://us.archive.ubuntu.com jaunty-updates/main Packages
Hit http://us.archive.ubuntu.com jaunty-updates/restricted Packages
Hit http://us.archive.ubuntu.com jaunty-updates/main Sources
Hit http://us.archive.ubuntu.com jaunty-updates/restricted Sources
Hit http://us.archive.ubuntu.com jaunty-updates/universe Packages
Hit http://security.ubuntu.com jaunty-security/universe Sources
Hit http://security.ubuntu.com jaunty-security/multiverse Packages
Hit http://security.ubuntu.com jaunty-security/multiverse Sources
Hit http://us.archive.ubuntu.com jaunty-updates/universe Sources
Hit http://us.archive.ubuntu.com jaunty-updates/multiverse Packages
Hit http://us.archive.ubuntu.com jaunty-updates/multiverse Sources
Reading package lists... Done

After the system successfully downloads data from the repositories execute "sudo apt-get dist-upgrade -y" from the shell prompt to update your Ubuntu OS to the latest available software. The update process may ask you questions for some of the software being upgraded due to significant configuration or OS changes. Once complete, ensure your system is up to date by executing "sudo apt-get dist-upgrade -y" a second time and you should see the following on your screen.

$ sudo apt-get dist-upgrade -y
Reading package lists... Done
Building dependency tree      
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

After all updates have been applied it is recommended that you perform a soft reboot of your server using the "sudo shutdown -r now" command from the shell prompt. This is to ensure you boot into any new kernels that Aptitude may have installed.