* Follows broad changes prompted by activist investor
* Garrett-Cox had already stepped down from board
* Investment oversight duties to be split
By Simon Jessop
LONDON, Feb 15 (Reuters) - Katherine Garrett-Cox is to leaveinvestment firm Alliance Trust after a shareholderrebellion last year saw her forced to accept a diminished rolein a wide overhaul of the company.
Garrett-Cox and the board mutually agreed she would stepdown as chief executive of its fund arm, Alliance TrustInvestments, on March 11, with responsibilities for running its5 billion pounds ($7.24 billion) in assets reassigned.
The move caps several months of change for Alliance Trustafter Garrett-Cox ceded defeat in a high-profile battle withactivist U.S. hedge fund Elliott Advisors, which wanted sweepingchanges to turn around a prolonged period of underperformance.
Those changes included cutting costs, selling out ofnon-core investments such as commercial property and changingthe company's board structure.
The latter had already resulted in Garrett-Cox stepping downfrom the Alliance Trust board and Chairwoman Karin Forsekeresigning. The decision to part company was an acknowledgementof Garrett-Cox's changed role, Alliance Trust said.
"Alliance Trust is undergoing significant change to improveboth its operating performance and investment returns," ChairmanLord Smith of Kelvin said.
"Alliance Trust is now moving swiftly to implement thechanges announced last year which are designed to enhanceshareholder returns. This process is well underway and it isclear to us all that the role of chief xxecutive of AllianceTrust Investments has changed significantly."
($1 = 0.6902 pounds)
(Editing by Jeremy Gaunt)
