Eggert Magnusson is to step down as West Ham's executive chairman, with Icelandic owner Bjorgolfur Gudmundsson to take a more hands-on role.
Magnusson will remain as the club's non-executive chairman - and is to appoint an executive team to handle the day-to-day running of the club.
But he will continue to be heavily involved and will keep his own stake in the club.
The shake-up is intended to take West Ham to the next stage of their plan to break into the top four in the Premier League, and includes moving to a new stadium.
The club insist the changes will have no impact on manager Alan Curbishley and his coaching staff, who will remain in control of all football matters.