BOSTON — Change is everywhere for the Boston Celtics this season. And it’s noticeable in many ways, big and small.

Point guard Kyrie Irving is gone, replaced by another All-Star in Kemba Walker.

The spot in the middle of the offense that belonged to Al Horford will now be occupied by free-agent pickup Enes Kanter.

Some returning players even look different. Fourth-year guard Jaylen Brown’s trademark flat-top haircut? It’s gone, replaced by a sleeker, low-cut style.

“It is a fresh start. We all see Jaylen Brown’s hair, right?” Marcus Smart joked during the Celtics’ media day Monday.

It’s all apropos for a team that despite having All-Stars like Irving, Horford and Gordon Hayward, as well as young talent like Brown and Jayson Tatum, woefully underachieved — victimized by a lack of team chemistry and public infighting.

Now Boston has gone from the team that was the favorite to take over the Eastern Conference following LeBron James’ departure to the Lakers, to a team that must discover a new identity this season.

The players that returned said they internalized the lessons from last season.

“I think you learn that nothing is just going to be given to you in this league,” Hayward said. “I think a lot of people just kind of handed us the trip to the finals and thought we were going to walk our way to the Eastern Conference finals. That’s obviously not the case and didn’t happen.”

It’s why Coach Brad Stevens said a roster that often may find itself playing four wing players and a big man has to find a different way to play.

But he said it will start with the same principles that helped take the Celtics to back-to-back conference finals in 2016-17 and 2017-18.

“I just think that all I’ve ever thought and believed about the game has just been reinforced,” Stevens said. “I think this team will have to play differently on both sides of the ball than we have. Not enormously different, but we’ll have to do things here and there.”

He said he has no big plans for training camp other than creating an environment to help this new group begin to jell.

“Our focus over the next couple of weeks is just getting ready to play with the right effort and togetherness. And that’s it,” he said. “At the end of the day that will give us the chance to be the best version of ourselves.”

A NEW LEADER?

If there is one thing Walker said about joining the Celtics, it’s feeling humbled.

He’s gone from playing his entire career with a Charlotte team that only made the playoffs twice during his eight-year tenure, to a team that always has championship aspirations.

“There’s sure to be expectations because of the organization,” Walker said. “We have a really good team so there should be expectations. I’m very excited about that. … I’m looking forward to trying my best to meet that challenge.”

WORLD CUP LESSONS

The Celtics have six players who competed for their national teams during this summer’s World Cup.

Walker, Smart, Tatum and Brown played for Team USA, which stumbled to a seventh-place finish. Daniel Theis suited up for his native Germany and newcomer Vincent Poirer played for France.

Despite the disappointing result for Team USA, Walker said he’ll carry lessons from it into this season.

“The sacrifices,” Walker said. “You have to make sacrifices when you’re on a team like that. I think that’s something that we’ll bring here. Guys have to make sacrifices. You have to sometimes be uncomfortable and you have to adjust sometimes to help your team win. And you have to take on different roles that you might not like.”

CONTRACT YEAR

The Celtics have until Oct. 21 to decide whether to extend Brown’s contract for another season or let him become a restricted free agent next summer.

Asked about his contract status, Brown said he’s not focusing on it.

“I think stuff like that will end up working itself out in the end,” said Brown. “So I’m just focused on this season and playing basketball. I think that’s my No. 1 emphasis. Then let the chips fall where they may.”

NO TANKING

Kanter endeared himself to many Celtics fans bitter about Irving’s departure by taking Irving’s former No. 11 jersey.

Kanter said he chose that number mainly because he wore it with Oklahoma City. But he also took a small shot at another of his former teams, the New York Knicks, when explaining why Boston stuck out to him in free agency.

“I just want to go out there and win,” he said. “That’s one of the biggest reasons I picked the Celtics. Because they never tank.”