Move the clef symbol down one line. Tenor and alto clefs are both denoted by the same symbol; it is the placement of the symbol on the five-line staff that determines the clef. In tenor clef, the center of the symbol rests on the fourth line (counted from the bottom up), while the symbol for alto clef’s center rests on the middle line.
Shift any sharps or flats in the key signature to one line below (or space, if the accidentals rest on spaces). Unlike music for transposing instruments, the key signature stays the same when only the clefs are switched.
Write each note one line or space below its original placement on the staff. Though changed, all the notes within the passage you’re translating should be the same relative to one another, so translate this way in order to make the process less tedious. The new written passage will appear lower on the staff but should maintain its original shape.
Think upward if you are having trouble getting used to reading the alto clef or don’t have time to come up with a written transposition. Middle C is on the fourth line in tenor clef and the middle line in alto, for example, so play the corresponding notes two steps higher than they appear written.
Play the passage in the new clef to ensure you have translated accurately. If a note sounds incorrect, check the original passage and see what the pitch should be relative to the others around it. Also make sure you have not missed any accidentals.