MANCHESTER (AFP) - Amir Khan believes he has been transformed in less than six months working with trainer Freddie Roach and on Saturday plans to show that improvement when he boxes Marco Antonio Barrera. The English lightweight faces his toughest opponent since turning professional after winning an Olympic silver medal aged 17 in 2004 and victory over Mexican Barrera would revive his career following a shock first defeat last year. Khan was obliterated in just 54 seconds by Colombian Breidis Prescott in September at the MEN Arena in Manchester, where he returns to face Barrera for the World Boxing Association (WBA) International and World Boxing Organisation (WBO) Inter-Continental lightweight titles. A win for Khan, 22, will lead to a shot at one of the four major world titles, something that seemed a long way off when he was flattened by Prescott. But Khan, whose parents moved to Bolton in England from Pakistan before he was born, changed trainers after losing to Prescott and has enjoyed the new regime under Roach at a gym in Los Angeles, California. Khan is also savouring the anonymity he has in America while training with Roach, who also coaches the world's leading pound-for-pound fighter Manny Pacquiao. "Moving away to LA was one of the best things I have done because I've moved away from all those distractions I had back home in England," Khan told AFP. "I can focus completely on boxing when I'm in Los Angeles. I live for boxing - I eat, drink and sleep boxing. No one knows me and I just get more space. "Barrera comes to win every fight and is a warrior. But we have the speed, power and height advantage which is what we're going to be using. "This fight is all about patience. Instead of me rushing in with my hands down and chin up you are going to see a new Amir Khan in this fight. "We have been working on loads of different things and I can't wait to show people and myself how good I am. "That little mistake in the Prescott fight has made me realise I can't go rushing in there. Training with Freddie Roach has made me much better. I am a better boxer now than I have been before, skill wise, strength wise and power wise." But Barrera will be the best opponent Khan has ever faced, even if the Mexican has had just two low-key fights since being unanimously out-pointed by Pacquiao in October 2007. Barrera, 35, is motivated by the desire to become the first Mexican to win world titles in four weight divisions after his success at super-featherweight, featherweight and super-bantamweight. "I will not retire until I make history as the first Mexican to win world championship belts in four different weight divisions," he told AFP. "I took this fight against a young fighter because I believe that when I beat a guy in his home town in front of his own crowd it's a double victory." Barrera needed stitches to repair a cut over his left eye caused by a headbutt in a warm-up fight on January 31. The cut has healed although the scar is still visible, but Barrera insists it will not be a problem. "The cut was on top of the eye, it was in the middle of both eye about an inch above. I've been sparring and I'm ready to fight," he told AFP. Nicky Cook, the English super-featherweight, makes the first defence of his WBO title against Puerto Rico's Roman Martinez while Enzo Maccarinelli, of Wales, disputes the interim WBO cruiserweight title with America-based Ola Afolabi on the same bill.