The Prequel Trilogy would be an easy remake.
Age up Anakin in TPM, give the movie some attitude with his hot rod racing and contrast this against the doctrinal Jedi Order. Cut Qui-gon and give Obi-wan the agency to take him under his wing and train him.
For AOTC, make Anakin more sympathetic with an express goal of freeing his mother and the rest of the slaves in the galaxy, which gives him justification for wanting more power for the galactic government to fight injustice.
ROTS stays with Anakin as he more gradually loses his humanity to wounds suffered as he fights battles to ostensibly bring the lawless planets of the Outer Rim under Republic security, but he gets word that his mother has died before he reaches Tatooine. The Jedi oppose him in believing that he has gone too far, and Anakin genuinely believes that Obi-wan and the Jedi would let the galaxy burn to uphold the status quo.
The Original Trilogy should not be remade. Therefore, the best way to go about that is to make an alternate Episode 4 and 5 which could exist alongside the originals instead of supplanting them, with the end of Episode 5 beginning a new branch of continuity which will overwrite the Sequels.
The story of Episode 4 would follow Vader as he searches for the Rebels in protecting the Empire he helped create. We see him maskless several times, a figure who has sacrificed everything to safeguard the galaxy from injustice. He recognizes that the Empire does evil, but he always has a justification ready at hand. After the destruction of Alderaan he has a crisis of faith in his Empire. He contacts the Emperor, who assures him that when he takes command of the station he will punish Tarkin severely for his rash actions. The battle with Obi-wan on the Death Star is presented without cuts, with new lines and slightly enhanced choreography where Obi-wan berates him for the destruction of a peaceful world, but Anakin eschews responsibility and blames Tarkin. In his final battle with Luke, Anakin realizes that the boy could actually destroy the Death Star and so intentionally misses Luke’s X-wing, allowing him to take the fatal shot. After his narrow escape, he believes that the Force left him alive so that he could overthrow the evil Emperor and set the Empire to rights.
Episode 5 shows the moment when Anakin realizes that Skywalker is his son, and the film documents his quest to capture him. He is plagued by visions where Luke rejects his offer and throws himself into the bottomless pit, and knows that the future is always in motion. When the pivotal moment is reached, Luke accepts Anakin’s offer and goes with him to the Emperor, and there the Emperor is defeated. However, at that moment Luke turns on Anakin and tries to destroy him. The attempt fails but Luke escapes back to the Rebellion and the Empire devolves into chaos and infighting.
Episode 6 chronicles Anakin’s attempt to win back his son, a son who views his father as evil incarnate. The Alliance has grown in a year so much that it now rivals the weakened Empire. The film contains the final battle between father and son, one trying to bring order to the galaxy through Imperial rule and the other attempting to revert the galaxy to a state of weakened democracy. Anakin finally convinces Luke that to dissolve the Empire would bring decades of chaos and unrest, so in the final battle Luke kills his father and takes Anakin’s place on the throne, ending the war and reconciling the Empire and Rebel Alliance. In the final scene Luke declares this union to be a theocratic First Order, ruled by an order of Jedi Knights and backed up by the power of the Imperial machine.
Episodes 7-9 detail the ruin of this theocratic republic, which takes the worst aspects of the Republic and the Empire and merges them into one. Ben Skywalker, son of Luke Skywalker, must discover in the netherworld of the Force a way in which to transform the government into something which upholds the original philosophy of the Jedi.