Ubuntu 11.04 has been released earlier today and people are frantically downloading it. However, if you already have an older Ubuntu ISO - maybe the one of the beta or alpha ISO of Ubuntu 11.04 - you do not need to download the whole ISO again. Instead, you can simply update the old ISO to a the latest stable release of Ubuntu 11.04 using zsync. In this post we will show you how you can do it from Linux and Windows machines.

As we are going to use zsync, we obviously need to have zsync installed. In most Linux systems, it is installed by default. However, if you are on a Windows machine, you will need to install it using Cygwin. Please refer to our guide to set up Cygwin in Windows.

If you are on Windows, copy the old ISO into the Cygwin folder. By default the Cygwin folder is at C:/cygwin/. You can paste the ISO anywhere inside that folder.

Now that we have zsync, start the Terminal (in Linux) or cygwin (in Windows) and navigate to the directory where the old ISO is located.

Before we start zsync, make sure that you have not renamed the ISO. If you have renamed it, change it back to the original name. Otherwise zsync will simply download the entite ISO again.

Now execute the command given below. If you have a fairly recent daily build or a beta, there should be not much to download.

zsync [PATH]

In the above command, replace [PATH] with the appropriate URL from the list below:

Ubuntu 11.04 32-bit http://releases.ubuntu.com/releases/11.04/ubuntu-11.04-desktop-i386.iso.zsync

Ubuntu 11.04 64-bit http://releases.ubuntu.com/releases/11.04/ubuntu-11.04-desktop-amd64.iso.zsync

Ubuntu Server 11.04 32-bit http://releases.ubuntu.com/releases/11.04/ubuntu-11.04-server-i386.iso.zsync

Ubuntu Server 11.04 64-bit http://releases.ubuntu.com/releases/11.04/ubuntu-11.04-server-amd64.iso.zsync

Kubuntu 11.04 32-bit http://releases.ubuntu.com/kubuntu/11.04/kubuntu-11.04-desktop-i386.iso.zsync

Kubuntu 11.04 64-bit http://releases.ubuntu.com/kubuntu/11.04/kubuntu-11.04-desktop-amd64.iso.zsync

Xubuntu 11.04 32-bit http://cdimage.ubuntu.com/xubuntu/releases/11.04/release/xubuntu-11.04-desktop-i386.iso.zsync

Xubuntu 11.04 64-bit http://cdimage.ubuntu.com/xubuntu/releases/11.04/release/xubuntu-11.04-desktop-amd64.iso.zsync