[1/3]Two girls walk past the entrance of the Six Flags Over Texas amusement park in Arlington, Texas July 23, 2013. REUTERS/Mike Stone/File Photo Purchase Licensing Rights, opens new tab NEW YORK, March 25 (Reuters) - Theme park operator Six Flags Entertainment (FUN.N), opens new tabon Wednesday announced a change in leadership on its board, naming Richard Haddrill as executive chairman. Last week activist investor Jana Partners told the company in a letter seen by Reuters that it wants the company to immed ...