Extending your range, especially in the upper notes and registers, requires knowledge of how to work your singing muscles and how to switch into other registers. This is something that takes practice, even if you're fortunate enough to have singing lessons. It's not usually something that comes perfectly right away.
So for exercises, just make sure that you pracise mastering both your falsetto and head voice. Do scales each day, and everyday you push yourself to the very top note. (Don't go too far, of course, so that it hurts or anything.) Another exercise you can do to help stretch out your range and try to correct any breaks between registers is sirens.
Oh, and yeah, the 'HA HA' thing is actually a good tip. It's kinda like what the sirens do. The A sound there is really what helps, because it's one of those sounds you use to help reach higher notes. (Not sure if you know about the importance of vowels in singing professionally, but open vowel sounds, like "ah", help create a nice air flow and don't clench up your muscles in your throat, so it's easier to let out more difficult noises.)

If you're unsure of anything I just said, feel free to ask. :yes

Meh, I have short arms, too..... XD

Yeah, a lot of people don't realise it, because he's most known for hitting those high notes, but Michael Jackson had a wonderful range. Supposedly near four octaves; I believe it. x_X

Hahahah, SAME. I ALWAYS sing in falsetto. It's pretty hilarious :P

I have a question... idk how much you need to know, but I'm not a chorus student, so I don't know a lot about my voice ect. All I can really tell yo is that my range is from E-flat2 to G4 (comfortably, its more like E2 to F4)

Anyways, my question, whenever I sing falsetto (which, my falsetto register starts at about C#4 or D4), whenever I sing the vowel syllables other than ee (like the japanese i) or ooh (like the japanese u), its really hard to get out and its really airy. Can anyone help this?

^ Rox, that's because those are air constricting sounds. How you go about getting more sound out is up to you. You can do one of the following:

a. Just learn to force out the sound......which, as you can probably tell, isn't the best option. Even so, it's the easier option for those who don't care to learn how to sing properly. But it will result in your voice always being pop (or maybe rock, if it's rougher sounding) oriented. ...Which, whether or not that's bad, that's up to you, of course.
b. Alter the sounds. Which, this is what you are supposed to do. It may sound a bit funny if you do it to the extreme, but it's technically correct and much better for your voice. When I say alter the sound, I mean, you need to turn, for example, the "ee/Japanese i" sound into a more open vowel, like "aa" or "oh", or even a very loose "eh" sort of sound. (I talked about this a bit in my response to Waterballoon.) These sounds allow for more air flow, and it will certainly help enable better range. As you get used to singing more correctly, too, this will also help with your control, making it easier to hold smoother notes of varying pitch.
The only "negative" point to doing this (I say "negative", because it's not necessarily a bad thing), is that you are altering the actual word, then, too. So, for example, instead of it coming out as "watashi ni", it'll be more like "watashi ne" (or however you choose to alter it). This also results in a very opera-like sound if you change the sound too much - since opera is a very professional style, and this is a very professional menthod. Again, this may be good or bad, depending on how you feel about that style, hah. But once you get the hang of how to use this technique, you can certainly play around with it and learn to alter the sound only slightly, just enough to be able to get more air out.

^thx!! Thats been bothering me for a while. :D