tritrust

but its not the build im talking abou when i run hexxit its 1.5.2 and it connects to the server i play on but when i run atb for some reason its at 1.6.4 and i have no clue how to get it to .1.5.2

so im trying to get on a server but it says its out of date and i need to downgrade from 1.6.4 to 1.5.2 but i have no clue how i tried to do it the normal vanilla minecraft way but it starts up then send me back to the launcher please help