tell application "System Preferences"
reveal anchor "passwordPref" of pane "Accounts"
activate
end tell
tell application "System Events" to tell process "System Preferences" to click button "Change Password." of tab group 1 of window "Accounts"
the button is part of tab group 1
the text following “Change Password” is not three periods, it’s option-semicolon (called an ellipsis).
Then the sheet that pops down is sheet 1, text field 1, 2, & 3, and again the button “Change Password.” with an ellipsis.