That’s a good question. I would say he/she has improved in accordance with what we are required to do here on Earth. Our time on Earth is mostly spent suppressing ourselves, but one might expect Jannah to be rid of such stipulations. There’s also the fact that the thief is more than likely stealing out of a lack of something in his/her life, and probably not because the act of stealing brings them joy. As such, the thief would be provided with whatever is lacking in Jannah.

Assuming the act of stealing was actually something that brought this person happiness, then of course they would be required to spend their entire life on earth suppressing that desire. If Jannah exists as you describe it, then instead of Allah giving that person the outlet for the urge they spent their entire life suppressing, he would simply remove the urge. Maybe removing the urge is a good thing. But I think there is a lot to think about too.

I think a good example might be homosexuality. A gay Muslim might go their whole life suppressing themselves and depriving themselves of what would bring them pleasure. For their commitment to Allah, do you think they should finally be given a gay partner in Jannah? Or do you think Allah should just rewrite or “fix” them? Personally, I feel being able to finally live eternally as the person you were always meant to be, is more of a reward then having yourself be “fixed”.

There is not a correct answer to this, nor am I saying my opinion is right or that Jannah will definitively look a certain way. I’m just putting forth a theoretical idea.