Chromebook on ver 76 but “can’t find any new updates.”

Trying to get hbomax to work on my chromebook. The website says I need at least ver 78 of chromebook to use hbomax, but my ver is 76, and can’t seem to find updates. I’ve tried going into the privacy settings to “reset the website” and tried dling Firefox, which I haven’t been able to figure out. I was thinking maybe my pc is too old and that’s why it won’t update anymore? Any help is much appreciated.