To get started simply select the remote collection you would like to update. Keep in mind Microsoft images cannot be updated by you only Microsoft. As seen below.
Your remote deployment however can be updated to change the applications based on need and or location. As seen below with your remote desktop collection selected click the update button and you will be prompted for which image to deploy out to your collection. Within the option you have two choices allowing users to be logged out immediately once the update is completed or allowing them 60 minutes to complete the necessary work and allowing them to save their data.
Select the template that you would like to use to update your remote desktop collection with. (As shown above). The update of your image will begin. This can take a few minutes. Once completed you can now publish your newly added apps out to your users as seen below. From the client remote up select update and the newly published apps will appear.
Success! You have updated your newly added applications.
By: Adnan Cartwright
Azure Trial: http://aka.ms/try-azure