The head joint of a flute must be set to a certain pitch in order to have the flute play correctly. Once this procedure is performed it should not need to be performed again unless there are some drastic changes to your headjoint.

Locate your cleaning rod (a) and head joint (b). Locate the head crown (c) and tone hole (d) on the head joint.
1.
Find the thin line (a) on one end of the cleaning rod. Place this end into the headjoint from the right until it stops. If you look into the tone hole you should see that the thin line rests in the middle of it. If it does, you do not need to make an adjustment.
2.
If the line is too far to the left remove the cleaning rod and go to step 4. If it is too far to the right go to step 5. 3.
4.
5.
Unscrew the head crown from the head joint counterclockwise no more than the distance of the difference you saw. Press the head crown back into the flute and go back to step 3. Remove the cleaning rod and tighten the head crown clockwise one turn and go back to step 3.