As for the latter, its new synopsis (via Rochi Shion) reads:
Thor's world is about to explode in Marvel's Thor: Ragnarok. His devious brother, Loki, has taken over Asgard, the powerful Hela has emerged to steal the throne for herself and Thor is imprisoned on the other side of the universe. To escape captivity and save his home from imminent destruction, Thor must first win a deadly alien contest by defeating his former ally and fellow Avengers... The Incredible Hulk!
When comparing the synopsis above to one that was first released, which you can read below, we aren't provided with a whole lot of new information. It's just worded differently. The only exception would probably be that Hela "steals the throne" of Asgard from Loki -- who only rules over the Asgardians because he is impersonating his adoptive father, Odin.
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Thor is imprisoned on the other side of the universe without his mighty hammer and finds himself in a race against time to get back to Asgard to stop Ragnarok – the destruction of his homeworld and the end of Asgardian civilization – at the hands of an all-powerful new threat, the ruthless Hela. But first he must survive a deadly gladatorial contest that pits him against his former ally and fellow Avenger – The Incredible Hulk!”
The cast features Chris Hemsworth in the title role for the fifth time; Tom Hiddleston as Thor’s adversarial, adopted brother, Loki; Idris Elba as the Asgardian sentry, Heimdall; Sir Anthony Hopkins again portraying Odin, Ruler of Asgard; Mark Ruffalo reprising his role of Bruce Banner/the Hulk; Cate Blanchett as the mysterious and powerful new villain Hela; Jeff Goldblum as the eccentric Grandmaster; Tessa Thompson bring the classic hero Valkyrie to life on the big screen; and Karl Urban will add his might to the fray as Skurge.
Thor: Ragnarok is directed by Taika Waititi, written by Craig Kyle, and will open in theaters November 3, 2017.