rowuk

The key to playing high is most often more subtraction than addition.
Assuming that you practice a fair amount (an hour a day or so) and have been playing for a couple of years, there is probably more in your playing that BLOCKS high range than things that you can add to play higher.
Step one is an analysis of how you play now. Can you play up to some high note and then nothing above comes, or does it keep getting thinner and thinner.
In both cases, you may have some body use issues. You need to learn about good playing posture. There are some very good tips for body use at the Monette web site, even if you don't own their horns or mouthpieces. I have also NEVER met a player with perfect breathing. That means we can all work on that and relieve tension issues allowing us to take a more relaxed BIG breath!

The first case generally means that you use pressure to play high (like most all trumpet players) and there is a point where you just squeeze off any vibration of the lips. If this is the case, you need to reduce the pressure especially on the top lip. Just try angling the trumpet down a bit.
Of course this can be a lot more involved, but without seeing you play, we can only assume that everything else is 100%.........................
If your range doesn't stop at one note but just gets gradually thinner, congratulations- you belong to a very seldom species of trumpet player!! All you need is better breath support and the Earl Irons slur book and you are good to go!
You will certainly have to work on other aspects of your playing to get that smooth liquid high register - I just can't diagnose anything on the internet. You don't know what to tell me, and I don't know what to believe even if you describe it because we do not know one another. A real (good) teacher will always be more efficient in a situation like this

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Whenever I feel blue, I start breathing again.

splinter

I like that idea, look after the pennies and the pounds look after themselves!! saying that I'm stuck on middle A

Tom Mac

High range is the 2000 pound elephant that refuses to leave the room. My personal philosophy is that my top (arpegiated, buttocks clinched, red face ) range should be a forth higher than the range I need to play any particular piece. So, if the literature that I'm playing requires a high c (2nd ledger line) I need to be able to play the f above that.

I use clark study #2 starting at the top of the staff g. I play this every day and stop at c. This takes me up to the octave g. By applying common sense practice and playing principles this routine has extended my "top range" to the 5th ledger line c (that I call "double high c"). Gigging range is g.

This is, however, only the start. You must also learn how to play the full range of the horn correctly (you guys know what I mean) so that when the music demands high notes you've still got them.

Oh well, my 2.1415926873 Cents on this subject.

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T. Mac

"Music is a funny thing when you really come to think about it." M. Davis