korrigieren
to correct
To find and improve mistakes in a text, calculation, statement, or action.
Der Lehrer korrigiert die Klassenarbeiten der Schüler.
The teacher corrects the students' exams.

to correct
Loading your saved state.
to correct
To find and improve mistakes in a text, calculation, statement, or action.
Der Lehrer korrigiert die Klassenarbeiten der Schüler.
The teacher corrects the students' exams.

Verbs that end in '-ieren' often come from Latin or French. In German, they are almost always regular (weak) verbs and form the past participle with 'hat' and the ending '-t' (e.g., korrigiert).
Hast du meine E-Mail schon korrigiert?
Have you already corrected my email?
The corresponding noun for this verb is 'die Korrektur' (correction). It describes both the process of improving something and the result of that process.
Der Autor hat die Korrekturen des Lektors akzeptiert.
The author accepted the editor's corrections.
In its main meaning, 'korrigieren' (to correct) is used with things that can contain mistakes. Typical objects are: 'Fehler' (mistakes), 'einen Text' (a text), 'Hausaufgaben' (homework), 'eine Rechnung' (a calculation/bill), or 'eine Aussage' (a statement).
Bitte korrigiere die Fehler in diesem Dokument.
Please correct the mistakes in this document.
When it is not about mistakes, 'korrigieren' means to adjust or fine-tune. In this context, the objects are often things that have a direction or state, e.g., 'den Kurs' (the course), 'die Haltung' (the posture/attitude), or 'eine Prognose' (a forecast).
Das Unternehmen musste seine Gewinnprognose nach unten korrigieren.
The company had to adjust its profit forecast downward.
The reflexive form 'sich korrigieren' (to correct oneself) is used almost exclusively in spoken language. You say it when you realize that you have just said something wrong and immediately correct it.
Wir treffen uns am Montag – ach nein, ich korrigiere mich, am Dienstag.
We're meeting on Monday—oh no, I correct myself, on Tuesday.
to change
'ändern' and 'korrigieren' can both mean that something is different afterward. 'ändern' is neutral: something is simply made different. 'korrigieren' is used when something was wrong before or did not quite fit, and you want to make it right. This is typical for texts, calculations, statements, or also a posture, attitude, or direction. Learners may confuse the words because a correction is often a change. But when no mistake is meant, 'ändern' sounds more natural.

Er hat den Fehler in der Rechnung sofort korrigiert.
He corrected the mistake in the invoice immediately.
Heute ändert die Kundin ihre Bestellung noch einmal.
Today the customer changes her order once again.