Is there any way around this?

we live in an apt. complex we are not very happy with. our lease ends the middle of sept. we only planned on payed half of septembers rent since thats when our lease was signed. we were not going to move, as the place is descent in sq. footage for what we can afford. however we just now stumbled upon an even better place that is in our price limit. we are supposed to move in on the 15th. now our apt. complex tells us however that in our agreement it says we are to let them know 2 months ahead of time that we are moving out. i find this hard to do when we didnt know until 3 days ago after finding this place and putting in an application that we were going to move. does anyone know the legalities behind this or if there is any type of stipulation to make an exception? please let me know! thanks.