In Project > Target > Build Settings > Architectures:
change the Architectures from Standard Architectures (including 64-bit) to Standard Architectures ,or if you want to support older devices, type
armv6 armv7 armv7s
in Others
Then, you can change the deployment target to lower versions (just type 4.0
or 4.3
in the Deployment Target box)
But why do you want to target iOS 4 still?