The initial objectives of Donald Trump are to force Iran to abandon Iran's missile-advancement projects and it's assistance to Syria, Hezbollah, Hamas, and the Houthis. Trump also wants Iran to leave Syria and Iraq and to not venture anywhere else. In other words, Trump wants Iran to be completely neutral at the least. Trump wants all of that so the US and Israel will be vastly more dominant in the region. The neocons want Russia and China to be without a strong military and economic ally in the area. It's a question of imperialism.
As for regime change, the American People don't want an Islamic, Theocratic dictatorship ruling Iran. Many Iranians agree. What most Americans want to see is a secular democracy. Some Americans want a neoliberal-capitalist government over Iran. The trend in the US, however, is toward greater social democracy (very strong welfare state with nationalization of natural monopolies). The trend in the US is also away from the neocons' permanent, violent, global revolution for capitalism masked as democracy (ravening wolves in sheep's clothing).