The Dolphins’ overhauled offense expects big things in 2013. That’s no longer news. The star players already have told us all about it. As for the defense? The personnel changes have been nearly as dramatic, if not the hyperbole. The Dolphins invested big money and high draft picks to upgrade the unit at all three levels. And their expectations, according to linebacker Koa Misi, are no different than their teammates on the other side of the football. “We can be great,” Misi said Tuesday at a community event with local grade-school youths in Hialeah. “We’ve got a lot of new guys. They’re trying to learn the defense right now. “The guys that they brought in to play in this defense and bring it to where we need to be, I think they did a good job in that.” Now in his fourth season, Misi is suddenly in a strange spot: Along with reserve Austin Spitler, he’s the longest-tenured Dolphins linebacker. Karlos Dansby and Kevin Burnett commanded most of the attention in recent years, but Misi is now a leader out of necessity. Dansby and Burnett are gone, cut after the Dolphins signed Dannell Ellerbe and Philip Wheeler as free agents. Misi said “everybody” was shocked by the release of two of the defense’s more dependable — and outspoken — players, but acknowledged it’s the nature of the NFL. Besides, Misi has more pressing concerns: His own future with the team is far from certain. He’s entering the final year of his rookie deal, and said Tuesday that the Dolphins’ front office has not yet approached him about an extension. When asked if his contract situation is on his mind, Misi said with a smile: “Yeah, you could say that.” Entering the second year in Kevin Coyle’s 4-3 defense, Misi said he’s more comfortable playing strong-side linebacker than he was in 2012, when he had 3 1/2 sacks and a career-high 65 tackles. Misi, who played on the line in passing situations and occasionally blitzed from outside linebacker in base alignments last season, wants to get to the quarterback even more in 2013. His goal for sacks is eight — which would nearly double his career total. He also wants to create more turnovers, which coach Joe Philbin has listed as a top priority for the defense. Misi forced three fumbles last season but couldn’t recover any of them. Still, Pro Football Focus ranked Misi as the league’s 10th-best outside 4-3 linebacker last season, giving him particularly strong marks against the run. He was flagged for a penalty just once all season. “Your coaches know what they want from you, and it just pushes you that much harder to get to that point,” Misi said. “I feel like I’m getting pushed a little bit, and I like it.”