how to add ARC in between of project

I am creating iPhone app and in between I need to use SDWebImage. For this I need to use ARC.

Any idea how to add ARC in between in project?

Note: In one file I have below content.

#if !__has_feature(objc_arc)
#error SDWebImage is ARC only. Either turn on ARC for the project or use -fobjc-arc flag
#endif

Where should I add -fobjc-arc flag?

Select Project Form Project Manager
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  Targets
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     Build Phases
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        Compile Sources
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            Select File that you Want to crate as ARC. (You can also Select Multiple File name from here)
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                    Press "ENTER" key
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                      Popup Box/Window is displayed 
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                            Write here - '-fno-objc-arc'
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                                And again Press 'ENTER' key.

Your selected file is being ARC.

If you are using xcode 4.6 then Select your target Target->Build Settingsand find Apple LLVM compiler 4.2 see in this section if Objective-c Automatic Reference Counting is set to YES, if not then just set it to YES. For older version of XCode you could change for Apple LLVM compiler 3.0

Change from build settings

Project->Build setting->Objective-C Automatic Reference Counting  SET YES

If you need to remove ARC then Go to  Project->Build Phases->compile sources then find your file Which you need to remove ARC then set compile source '-fno-objc-arc'

In top of xcode

edit->refactor->then chose convert to Arc

try this