You need to get a coalition going. Normally what happens is that it is the same people who attend these AGM's and everything gets past just the way it is without much change. One or two voices are lost in the wilderness. Get enough of the dissenters to go, you usually find they are the ones that don't bother going because they think everything will get passed anyway, and use your collective voices to sway the fence sitters, the ones who vote with the consensus.
Don't argue or loose your temper at anyone, use facts and sound arguments. Use the 'chair' to get the hecklers to be quiet, if he can't do that then he isn't much good so put up a vote of no confidence

Put your arguments and ideas to some of the committee in a conversation before the meeting, if you can. Don't tell them that is what you are going to bring up at the meeting, just test their individual thoughts away from the rest.
You may not get everything in one go but you start to undermine the status quo and as time goes on you may get all of your changes if you stick at it.