You changed your order = you placed a new order in addition to...

You changed your order = you placed a new order in addition to your first. For example: You're first inline for 10,000 at 33c... you then decide to change it to 20,000. The initial 10,000 remain but the additional 10,000 will be added behind those who've already placed orders at 33c. So you now have 2 orders at 33c. You get your position in line ranked on when you place the order - not how much you want. You can't change your mind as that wouldn't be fair. I.e. you can't place an order for 1 share then decide to upgrade that to 100,000 because you detect a swing in movement. If there were no others in line behind your initial 10,000 buy order - then yes, it would change to 20,000.