All you need to do is follow this link.
Or, if you’d prefer to sign up for the iHeartRadio All Access trial on your Android or iOS device, just launch the app, tap the gear icon located in the upper left-hand corner of the screen and tap the Upgrade button!
Note: One free trial is permitted per iHeartRadio account, credit card, Apple ID, or Google Play Store account.
For more information on how to sign up for a free trial on your device click here.
To read about subscription terms and conditions click here.