Postecoglou joined Tottenham after a successful spell at Celtic
Spurs are fifth in their first season under the Australian but have lost their past three games, including a 2-0 defeat by rivals Chelsea on Thursday.
Postecoglou, who was unbeaten in his first 10 league games as Spurs boss, has attempted to implement a more entertaining style during the campaign.
"I've got to change this squad," he said.
"I have to because I've got to build a squad I think can play our football.
"For that to happen, there has to be exits."
Tottenham have made significant signings since Postecoglou took charge following spells under more pragmatic managers in Jose Mourinho, Nuno Espirito Santo and Antonio Conte.
Midfielder James Maddison, forward Brennan Johnson, defender Micky van de Ven and goalkeeper Guglielmo Vicario were all brought in while the club have also let experienced players such as former goalkeeper and captain Hugo Lloris, plus defenders Eric Dier and Davinson Sanchez leave.
"We need change. Change has to happen," said Postecoglou, whose side play Liverpool on Sunday.
"You can't want to alter your course, quite dramatically for this club because we went down a certain direction and now we're pivoting to a whole different direction, and expect the same people are going to be on that.
"It's just not going to happen.
"We've had two windows and we've had some development of players, for sure, but when I say we've still got a long way to go, that's what I'm talking about."
He added: "It's not for the want of trying. It's just that we're going to play a certain way, we're going to train a certain way, we're going to have a certain mindset and that's not for everyone.
"And the same way, whether it's Liverpool or Arsenal, if you look at the beginning of their journeys, by the time they win the competition or have success, the team's almost unrecognisable."
-- Courtesy of BBC Sport