Serle is joining Orion Media,the company launched by former Chrysalis Radio boss Phil Riley to buy Global Radio's Midlands radio stations, as its first commercial director.
Stacey, in addition to her radio duties, will also head Bauer's TV sales and its 17-strong cross-media brand solutions team. Darren Khan, the television sales director, will now report directly to Stacey.
Stacey's promotion and Serle's departure follow recent changes at Bauer which included the departure of Tim McCabe, its associate director of brand solutions.
Rebecca Lisica, the head of business planning and development, takes on the new role of cross media business development director in the brand solutions team with a remit to develop a deeper understanding and closer relationship with advertisers.
Paul Keenan, the chief executive of Bauer Media, said: "Karen's extensive experience will strengthen one of the most innovative and creative teams in media today."
Stacey said: "Bauer Media is in the unique position of being able to offer highly-effective, innovative, cross-platform solutions that really make a difference for our advertisers."