First things first, I want to pass along to you some real basic exercises that I still use to maintain chops strength and focus - long tones, scales, and tonguing exercises.
The first thing I want to talk about is long tones. For two weeks, start your practice routines with these. Take as big of an easy breath as you can, and starting on a low C, play the note softly, in control, and consciously working to reduce mouthpiece pressure. Repeat. (Two breaths/two long tones per note.) Then, after a short rest (45-90 seconds) move down one half step and do the same thing. Do this all the way to low F#. Play the note until you are out of air, and then keep playing, squeezing as much air out of your lungs as you can. Once you get to low F#, move back up chromatically and finish on the low C.
This develops 4 things: Chops focus, chops strength, breath capacity and breath control.
Next exercises - articulation. I think that these are often approached incorrectly by inexperienced players, but if approached correctly can bring a lot of strength and focus to your chops.
One of the things I work on, are getting 4 fast, sharp, clean, crisp articulations in a row, and I do all of these right in the staff, usually starting on a second line G. Over and over and over, focusing on getting the articulation clean, and consciously keeping in mind reduced mouthpiece pressure. Rest often.
Another exercise I will do, usually as part of a warm-up is to play single-tongued legato 16th notes, 8 beats per pitch, starting on G in the staff, working down chromatically to low F#, then climb back up to 3rd space C, then back down to the starting G. The idea here is to play through as many pitches on one breath as possible. Take short breaks if you need to keep your chops from burning out, but again, focus on the clarity of the articulation (even legato needs to be clear - just not as sharp as a standard attack) and in making sure that you aren't pressing too hard on the mouthpiece.
Another exercise I do is to single tongue up and down a 1 octave chromatic scale, slowly at first, then picking up speed. The idea here is clarity and cleanliness, and making sure that your fingers and tongue are in synch.
By this point you are probably scratching your head thinking, "what in the heck does this have to do with range?" Well, a lot really. By focusing in on those fundamentals between articulation and sound production, a couple of things happen with your chops. The first thing is that you stop using so much mouthpiece pressure while at the same time improving your chops strength and focus. The articulation exercises also promote breath control, and air efficiency, which also helps to promote chops focus and strength.
The bottom line to this ramble I have posted to you is that there is no magic pill to better range, but I believe that incorporating these things into your daily practice, if you can strengthen the foundation, the range, at least to high C anyway, (meaning 2nd ledger C above the staff) will soon follow.
Last thing - it's important to remember that overworking your chops can also be detrimental. If for some reason you start to practice and things just aren't coming together or you chops aren't focusing (still happens to me from time to time) put the horn away for the day (if you can) and go do something else until the next day.