As you go higher in the range of notes the flute can play, the fingerings become more complicated and less intuitive, but gaining confidence and comfort with the extreme high register is easy to do if you take the right approach.
When you're trying to learn a new note, try moving back and forth between the new note and a note you already know and are comfortable with. Start slowly, and only increase your speed when you can move smoothly from note to note without any hesitation. Ingrain a feeling of ease, rather than trying to push for speed.
Below is a basic template that you can use for practicing high notes. (Click the image to download a printable PDF version.) Use any two notes you like, and remember that a few minutes each day of focused, purposeful practice are more useful than a longer period of halfhearted effort.