The version number you listed isn't MSN 8.5 (and if i'm being picky, there's no such thing as MSN 8.5)
What you have is Windows Live Messenger (abbreviated to WLM) and you have version 2009, also known as version 9 and version 14
You can use the skinning feature of Messenger Plus! Live to remove the ads, or I believe that A-Patch also removes the adverts
These are both third party add-ons for WLM.
Messenger Plus! Live is the add-on that this support site is for, you can download the latest version
here and then investigate skinning, or take a look
here to find skins which you may like (if you wish to change the look of messenger), as some also have a 'secret option' to remove the adverts