Shoutbox

1. Click on the Start button of Windows (bottom left button)
   
2. Select the Control Panel
   
3. Now click on "Add/Remove Programs"
   
   
4. Search for "Windows Live Essentials" in the list of installed programs and select it
   
5. Click on the "Remove/Repair" button
   
6. Choose to uninstall
   
7. Select "Windows Live Messenger" in the uninstaller

From here on, it could be that you can't do the suggested stuff because you can't find some entry. In that case just proceed to the next block.

1. In the same "Add/Remove Programs" dialog, search for "Windows Live Messenger" and select it
   
2. Click on the "Remove/Repair" button
   
3. Choose to uninstall
   
4. Follow the instructions

1. In the same "Add/Remove Programs" dialog, search for "MSN Messenger" and select it
   
2. Click on the "Remove/Repair" button
   
3. Choose to uninstall
   
4. Follow the instructions

Now everything should be uninstalled (I hope). To make sure:

1. Open Windows Explorer
   (you can do this quickly by pressing <WIN><E> at the same time; <WIN> is the Windows Key on your keyboard, between <CTRL> and <ALT>)
   
2. In the left pane navigate to "C:\Program Files"
   
3. Search in that tree for the folder "MSN Messenger"
   
4. If it exists, delete it: right click the folder and choose "Delete"

Now you can re-download and re-install WLM.

1. Go to http://messenger.live.com
   
2. Download the new Messenger setup and run it

Although, I must say that I find it a bit strange that Messenger didn't uninstalled the previous version by itself though. I thought it would...