First things first. Bent spring hanger equals bent axles. So your going to need to find a good welder/fabricator to fix things for you. Then, upgrading axles is pretty simple. You place an order for new axle tubes with the exact same dimensions as the old ones. Order them complete with brakes etc and springs. That way,,other than adding bronze busnings your ready to bolt them on. Order new tires,wheels, and lug nuts and bolt them on. Be aware you may not have sufficient clearence between axles and under the trailer to actually do all this without raising the trailer some. It may also mean you have to have new spring hangers installed to increase axle spacing.