No we do not have to update the number of stars in the Universe, and no they did not "discover the Universe has 20 times as many galaxies as we thought".
This discovery is actually detecting young, numerous galaxies that we believed were there but could not see. In fact, it is simply confirming the accuracy of the existing Lambda-CDM model.
When galaxies first formed there were very numerous small galaxies that merged into fewer more massive galaxies that we can easily see (since they are brighter and closer, being more recent in time). We knew those ancient small galaxies were out there, waiting to be detected. A nice discovery, but no new revelation is involved at all.