http://technet.microsoft.com/en-us/library/jj612867.aspx:
Yes you heard it right, its possible now just follow some of these simple steps:
Sí has oído bien, es posible ahora sólo siguiendo algunos de estos sencillos pasos (en plan teletienda):
1). Activate your copy of windows with a MAK or KMS method (Since MAK keys are harder to find and are used up early so i will tell you only KMS method!).
2). To activate windows using KMS server, run Command Prompt (CMD) as Admin and enter the following in the given order:
(Abrir terminal en windows8: llevar ratón a la esquina izquierda abajo, clic derecho->abrir terminal admin. O ratón arriba derecha, buscar en aplicaciones: cmd)
slmgr /ipk XXXXX-XXXXX-XXXXX-XXXXX-XXXXX
(XXXXX-XXXXX... para obtener un código válido para 180 días:
http://technet.microsoft.com/en-us/library/jj612867.aspx)
slmgr /skms fourdeltaone.net:1688
slmgr.vbs -ato
slmgr /ckms
NOTE:
1). XXXXX is the Generic Volume key for Windows 8 Pro.
2). If the server is running then you will be activated for 180 days.
More working KMS servers:
lunar21.no-ip.org:80
lunar21.no-ip.org:1688
kms.columbia.edu:1688
For "lunar21.no-ip.org" server, set the time zone at GMT+02.00 Cairo or something no further than 4 hours away from the Cairo timing, then synchronize the time.
3). Visit this official site and get your legit free key for an upgrade to Windows 8 Pro with Windows Media Center: (Sólo hasta el 31 de Enero de 2013)
http://windows.microsoft.com/en-US/windows-8/feature-packs4). Now right click on extreme lower left corner of your screen and go to "System".
5). Click on "Get more features with a new edition of Windows" and select "I already have a product key", enter the key and follow the online procedure to make your Windows legitimately activated!
(El código obtenido en el paso 3, puedes tardar en recibirlo más de un día. Que se instale Windows Mendia Center puede tardar, paciencia)