ändern
to change
To alter something so that it becomes different from before; to make a modification.
Ich muss den Termin für unser Treffen leider ändern.
Unfortunately, I have to change the date for our meeting.

to change
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to change
To alter something so that it becomes different from before; to make a modification.
Ich muss den Termin für unser Treffen leider ändern.
Unfortunately, I have to change the date for our meeting.

It is important to distinguish between 'ändern' and 'sich ändern'. 'Etwas ändern' (to change something) is transitive and means that a person actively changes a thing. 'Sich ändern' (to change) is reflexive and means that a thing or person becomes different by itself.
Er hat seine Meinung geändert.
He changed his mind.
The construction 'etwas an etwas ändern' (to change something about something) always uses the preposition 'an' followed by the dative. It is used to express that you are changing a specific aspect of a larger thing.
Kannst du etwas an diesem Satz ändern? Er klingt nicht gut.
Can you change something about this sentence? It doesn't sound good.
The verb 'ändern' is often combined with things that can be adjusted or corrected. Common collocations are: 'einen Plan ändern' (to change a plan), 'einen Termin ändern' (to change an appointment/date), 'die Adresse ändern' (to change the address), or 'die Reihenfolge ändern' (to change the order).
Wir müssen den Plan für das Wochenende ändern, da Regen gemeldet ist.
We have to change the plan for the weekend because rain is forecast.
to change
'ändern' and 'verändern' are often very similar. Both mean that something becomes different or that you make something different. 'ändern' is often used for specific points, rules, plans, appointments, or texts. 'verändern' places more emphasis on the new state or on a larger change, for example with people, places, or situations. Sometimes both are possible, but they do not always sound the same. Learners can easily confuse them because there is also 'sich ändern' and 'sich verändern'. As a simple guide: you are more likely to use 'ändern' for an appointment or a sentence; a city or a person is more likely to 'sich verändern'.

Kannst du bitte die Uhrzeit im Plan ändern?
Can you please change the time in the schedule?
Nach der langen Reise hat sich mein Bruder sehr verändert.
After the long trip, my brother changed a lot.