For MuseScore 3 users, see Clefs
Clefs are created or changed by dragging a clef symbol from the clef palette to a measure or another clef. Use F9 to show or hide the palette sidebar.
Drag a clef from the palette onto a clef in the score. You can also drag a clef from the score to another clef of the score by using Shift + leftMouseButton + Drag.
Drag a clef from the palette onto an empty part of a measure. This creates a clef at the beginning of the measure. Drag a clef to a particular note to create a mid-measure clef. If the measure is not the first measure in the staff it is drawn smaller.
Select a clef and press Del.
Note that changing a clef does not change the pitch of any note. Instead the notes are moved.