- Launch your Xcode project
- Go to the menu: Project --> Edit Project Settings
- Go to the "General" Tab
- At bottom of the General Tab - for "Base SDK for All Configurations" select "iPhone Device 4.0" (or "Latest SDK" if available)
If you want to still suport iOS 3.x devices:
- Go to the "Build" Tab
- Select the Configuration: "All Configurations"
- Enter the search term: "iPhone OS Deployment Target"
- In the "iPhone OS Deployment Target" field: select "iPhone OS 3.0" (or your appropriate lowest SDK you want to support)