For a general change:
* mudança: This is the most common and general word for change.
* alteração: This word is more formal and often used for changes that are more specific or technical.
For changing something physically:
* trocar: This means to exchange or swap something.
* mudar: This means to change something from one state to another.
For changing currency:
* trocar: This means to exchange currency.
For changing one's mind or opinion:
* mudar de ideias: This means to change one's mind.
* mudar de opinião: This means to change one's opinion.
For a change in the weather:
* mudança: This means a change in the weather.
* alteração: This word is also used for changes in the weather.
The best Portuguese word for "change" will depend on the specific situation.