How do I downgrade my minecraft back to 1.6.6?

Well recently I was playing happily on the 1,6.6 beta version then I went out with my mum, then when I returned it was on 1,7 me not knowing anything I simply updated and then obviously I couldn't connect back onto the server because it is still 1.6.6 so can someone give me the 1.6.6 bin files for me to downgrade.