Spurs have enjoyed moments of promise in Postecoglou's first season in charge, but they have experienced a significant drop-off in recent weeks.
Tottenham's hopes of achieving a top-four finish have been dented by a run of three consecutive defeats to Newcastle United, Arsenal and Chelsea.
Postecoglou has already offloaded the likes of Hugo Lloris, Eric Dier and Lucas Moura in his first two transfer windows, but he is now set to sanction another wave of departures in a bid to take Tottenham to the next level.
The Tottenham boss was asked whether he needs to make tough decisions over the playing squad in Friday's pre-match press conference ahead of the upcoming clash with Liverpool
Postecoglou preparing for summer exits
Postecoglou told reporters: "We've already made tough decisions, we let some experienced players leave the club at the beginning of the year, some by choice. But again, I feel like if we're really going to change, that means change. You have to make decisions.
"Some of those decisions aren't that tough because whether it's a player or a staff member, they realise it themselves and say, 'You know what, I've got a better path somewhere else and you've got a better path here.'
"So they're not that tough, but some of them you have to make just because of change, not necessarily because they don't fit in the picture but you still have to change.
"I've got to change this squad, 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.
"I can't just keep everyone here and keep bringing in players. So sometimes you let people go who you think 'he's a good player' but how am I going to change if I don't do that."
According to The Telegraph, Richarlison is among those Postecoglou could look to move on in the summer transfer window.
The report claims that Tottenham will listen to offers for the Brazilian, who is believed to be attracting interest from the Saudi Pro League.
Richarlison could be sold this summer
Richarlison has scored 10 goals in 27 appearances this season, but he is not a guaranteed starter in Postecoglou's lineup.
The 26-year-old has had to settle for 18 Premier League starts, with Son Heung-min often utilised as the central striker.
Tottenham are also set to consider proposals for defender Emerson Royal and midfielder Pierre-Emile Hojbjerg, as Postecoglou looks to make room in his squad for new arrivals.
The North London club are keen to retain the services of Yves Bissouma, but they could reconsider their stance should they receive a significant offer in the summer window.