Colin McGranahan

Best Buy continued its management upheaval Thursday as its founder, Richard Schulze, said he would leave the board earlier than expected.Schulze, who started the company more than 40 years ago, also said he was looking at ways to sell his 20.1 percent stake in the retailer, worth about $1.3 billion.It is the latest personnel retreat for the retailer stemming from the abrupt resignation of the former chief executive, Brian J. Dunn, in April. Last month, the board reported that Dunn had had an inappropriate relationship with a female employee. An internal investigation revealed that Schulze had known about the