Let's say a person takes the deal, goes before the judge, the judge sides with the prosecutor, and the judge gives the defendant six months in prison. At that

Let's say a person takes the deal, goes before the judge, the judge sides with the prosecutor, and the judge gives the defendant six months in prison. At that point can the defendant say, "actually, thanks but no thanks, I want a jury trial"? Or is the defendant bound to the sentence once he agrees to go before the judge?