BlackBerry has not opened "Beta Zone" access to all developers. Currently only option available for gNewsReader is to use BlackBerry app world sandbox. To enroll to beta program first get your bbid (email used as login to app world) registered with sandbox by sending it to the developer support email address.
To install the betaupdate.
swipe top from app world for options menu
click on development mode
in the content id field enter 21200129 and hit "Test Content"
This will take you to install page
you will also need to put the phone in "Development Mode" using options
under Settings -> Security and Privacy -> Development Mode
might take few hours for changes to appear
Also the payment step shown here is testing purpose only it will not actually bill you. its only a mock verification step.