Hi Aminu,
You can update to the latest Beta version only via the ReachView app. Your unit needs to be connected to the Internet to be able to check for updates. To receive information about Beta releases, you will need to subscribe to the dev updates in the Firmware Updates tab. The detailed information about the updating process can be found in our Updater docs.
Currently, all of the fixes and improvements from the latest 26 Beta 2 firmware version are added to the latest stable 26 Firmware. You can check the full changelog in this community forum thread.