Yamaha 400 Series Owner's Manual page 10

Tuning
Since changes in temperature and humidity can affect the instrument's pitch, blow some air through the instrument to warm it up before tuning.
Tuning is accomplished by sliding the headjoint
slightly toward or away from the body.
* Pull out on the headjoint to lower the pitch
10
and push it in to raise the pitch.
Piccolo/Flute
Headjoint
On the alto and bass flutes, tuning is accomplished
by sliding the U-joint slightly toward or away from
the body.
Body
* Do not adjust the space between the headjoint and
U-joint. Doing so will degrade the pitch balance,
making it difficult to tune the instrument.
Alto Flute/Bass Flute
U-joint
Body
Headjoint