Alan Howard, whose hedge fund once managed $40 billion, is stepping down as chief executive to focus on trading in another move to revive the struggling firm he founded. Aron Landy, currently the chief risk officer for Brevan Howard Asset Management, will take on the CEO role, the firm said Tuesday in a U.K. regulatory filing. “Going forward, Alan will focus on his own trading activities and will of course remain closely involved with the firm’s investment strategies,” according to the filing.