To set the Application Icons for all IOS version (6.0 to 9.0) you can use this road map.

• Add an Asset Cataloge to your IOS project.
• You can choose your target devices on property pages for AppIcons.
• Add all your Icons to AppIcons. 
• In Info.plist file, you can select your Asset Cataloge under Universal/iPhone/iPad Icons tab.

You can find more details here