May 21 (Reuters) - Kontoor Brands said on Thursday it had agreed to sell its Lee denim brand for up to $1 billion to Authentic Brands Group, as the apparel maker streamlines its operations and focuses on higher-growth brands such as Wrangler. The deal comprises an initial $750 million payment and a potential $250 million earnout tied to future performance under Authentic's ownership, Kontoor said. Shares of Kontoor were up 1% in premarket trading.