iphone 6 dock problems.

okay surely im not the only one experiencing this, i have searched everywhere but found nothing.

i cant change the 4 apps in the bottom dock. i want to put messages in instead of mail.

i have just got an iphone 6 today after 4 years of android and this problem is infuriating me. i remember you could just hold and then move apps around as you wish. but now it seems the dock apps are locked???? ***? there is no conceivable situation where locking the 4 dock apps would be a good idea.. if apple has done this i might be very close to taking it back.

please someone tell me this isnt the case and i am just doing it wrong.