I have been playing Horn for 5 years, and am first chair in my High School's Winds Ensemble. Because I am first, i am expected to play in my higher range often. But i am having trouble getting anywhere above a G right above the staff consistantly, and i have to play A's right above that. Does anyone have any tips to help with my higher range? Thanks!

Two suggestions for you.

One) Here is an exercise you can do. Twice a day, once in the morning and once in the evening (before you go to school and sometime when you get home before you go to bed).
Start on a low F (three ledger lines down from the treble clef). Play the F as a long tone as long as you can up to 20 seconds. Move down a half-step to G# and do the same thing, continuing to low C. Then go up to middle C (1st ledger line below the treble clef) and play a slow chromatic scale up to C (third space) and come back down chromatically. Move to C# and go up chormaticaly and back down. Move to D (up & down), D#,E,F,F#,G,etc. When you can't go any higher -stop.
In the evening session do not do any warm downs after playing your highest note.
YOu should see improvement by a half step every 3 ro 4 days.

Two) Get a copy of Walter Moecks Warm-ups for French Horn. It costs about $2.50. If your local music store doesn't have it you can find it many places online. Use it - everyday.

That's a great exercise for slowly extending your range both upward and downward. But also in order to get it to work make sure you are practicing correctly. A lot of beginners have range problems that actually stem from breathing problems and this can carry on for several years without being addressed by a teacher. If you don't have a teacher, get one. So air wise, when you are approaching higher notes, make sure you follow your air through without letting it thin out. Maybe you've heard shouts of suggestions "MORE AIR!!! MORE AIIRR!!" for high notes. Really, the air that does the work for you. Not that you need more of it, it's just how you use it. And always double check on yourself that you're not relying on mouthpiece pressure or squeezing your lips to squeak out high notes. They should be round and full tones just like your middle register, and not pinched.

Also, check out YouTube for a few range-expanding ideas. Trumpet players and tuba players in particular have some great ideas you can learn from, so check out some channels. Just don't listen to little kids, look for the pro-looking guys.