It isn’t all that easy. Not that easy at all.
You can turn to settings in Windows and turn off personal ads, the second option is via your MS account settings.
9 ways to block personal ads: http://computerworld.nl/it-beheer/75146-9-manieren-om-persoonlijke-ads-te-blokkeren
(google translate from Dutch).
But there must be a more elegant way - I understood this has to be performed per app.
Who has all the know-how and instructions for Windows 8.1?
polonus