Help & troubleshooting for channels on your Roku device, including adding/removing channels, logging in to, authenticating, or activating a channel, channel-specific playback issues, assistance contacting channel publishers to report issues, and adjusting channel-specific settings.
The HBO app will upgrade to HBO Max if you update the Roku's software. Go to Settings/System/System Update on the left side of the homepage. After the app has updated, restart the Roku. The app should be updated when the Roku restarts. You'll know it updated if the black HBO app tile is now purple and says HBO Max.
You shouldn't even have to log in again when you update.