Forest went down 2-0 at Brentford on Saturday to stay in the bottom three with one win from their opening nine Premier League games and Glasner said change was needed.
"We have to accept it's not good enough," Glasner, who enjoyed great success at Crystal Palace in the last two seasons before moving to the City Ground, told a press conference.
"If we lose four of the last five games, it's not good enough. And that's why for me, it's now time that we change things, that I change things, and that's what I will do."
Forest have churned through managers since Nuno Espirito Santo parted company with the club last September, since when Ange Postecoglou, Sean Dyche and Vitor Pereira have all come and gone.
"I feel I could see a few things from day number one. I feel now maybe I made too many compromises in some stuff, and it's always compromises," Glasner said.
"It's a clear way. I will tell (the players) what we want to do, what we have to do, and if the players buy in, I think we can have a turnaround and, if not, the sixth manager (since the start of last season) will come in."
Asked if he was concerned about his future, Austrian Glasner said: "I have no concerns. For me, I go home and have breakfast with my family. It's not the worst situation. Nobody needs to have pity with Oliver Glasner or with the manager.
"If I want, I could start in two weeks somewhere else. I won't do it. But, you know, the players, the staff, they remain in the same situation. And it's the same, sorry for the word, shit situation that the club had last year.
"So you need to change and rebuild from the bottom to the top. And this is clear for me. And this is what I will do. And without any compromises. Zero. Zero. And if these things don't work, they will let me know.
"I didn't come to Nottingham because I was bored at home. No, I came to Nottingham to succeed. I came to Nottingham to get the visions of the owner and the fans and the club to reality. And therefore we need to have a bigger change than maybe I thought, to be honest."
Glasner also said he did not need to "be loved" by his players and that he had turned down a request from one player to travel back from London alone.
"I was asked if a player can drive home alone. I said no," Glasner said. "I have no understanding (why) somebody wants to go home on his own today, from London to Nottingham. No, go with the bus like everybody else. No extras. No extras."