You can upgrade it regardless of which Astro box you're using now. (Except Njoi ones of course)

Assuming you're not living in MDUs (apartment, condo) that uses the outdated centralise dish system, you can proceed to upgrade.
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To enjoy this, here some conditions you need to know:
1) Must subscribe to HD-PVR service (worth RM25/month if a-la-carte) to watch any 4K UHD channel. If you've already subscribed that, then there's no additional monthly charges.
2) Must have UHD TV to watch any 4K UHD channel (e.g. ch780).
3) >10Mbps Internet connection is required. Otherwise, some functionalities will not be available, such as cloud recording, Video On Demand, "Play from Start" feature... If your Internet is slower than 10Mbps, slow loading, buffering and poor streaming quality issues may occur.
4) 24 months contract applies, or up to RM1600 penalty charges if terminate within contract period.
More info:
https://www.astro.com.my/ultraSituation:
i)
Don't have 4K UHD TV:
When tune to any 4K UHD channels, only the audio from that channel can be heard, and the screen will appear black and HDCP error message will show on screen, exactly like this:

You can still can access to SD and HD channels as what you have now.
ii)
Don't have Internet, or
not connected to the Internet (either via WiFi or Ethernet):
Features as cloud recording, Video On Demand, "Play from Start" feature, will not be available.
iii)
Internet slower than 10Mbps:
When you stream Video on Demand content or use Play from Start feature, you might experience slow loading, buffering and poor streaming quality issues may occur.
yup for my case, its free to get ultra box while I need to pay for PVR box.