Well, if u are having MPEG2 set top box u will get a sms from tata sky about the upgrade offer.
Call the customer care and ask them, if the upgrade offer is not available right now for u (in case your set top box is MPEG2), don't worry u will get that offer when they start migrating the channels to MPEG4 which u have subscribed or is a part of your package/regional channels.