From Longman Business Dictionary
oustoust /aʊst/ verb [transitiveT] journalism1to force someone to leave a job or important positionProfit margins collapsed and Martinez was ousted as chairman.
oust somebody from somethingtwo top executives who had been ousted from the board
2if one company or product ousts another from its market position, it becomes more successfuloust something from somethingCotton eventually ousted wool from its dominant role in clothing production.