You can upgrade from the limited trial mode, to the unlimited mode anytime, by tapping the shopping bag icon in the upper right corner of the main screen.
Or by tapping the word "buy" in the main menu (access upper left).
Or by tapping on one of the unlimited mode only features I.E. - repeat play, sleep timer, alarm clock or by attempting to name and save an equalizer profile for later recall.
Your current price, reflecting all available discounts will display prior to purchase.
There is an automatic 15% discount for upgrading within 5 days (120 hours) of registering.
And an additional 5% for each friend you share with and who registers within your five day window will be tracked and applied as well.
You can check on the status of your friend registrations through a link in the main menu.
Also see the topic: