Unable to convert classes into dex format. How do I locate duplicate jar files and edit?

CommandInvokationFailure: Unable to convert classes into dex format. C:/Java/jdk1.7.0_11\bin\java.exe -Xmx1024M -Dcom.android.sdkmanager.toolsdir="D:/Android/sdk\tools" -Dfile.encoding=UTF8 -jar "D:\Unity 3D\Editor\Data\PlaybackEngines\AndroidPlayer/Tools\sdktools.jar" -

stderr[ Exception in thread "main" java.lang.UnsupportedClassVersionError: com/android/dx/command/Main : Unsupported major.minor version 52.0 at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:791) at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) at java.net.URLClassLoader.defineClass(URLClassLoader.java:449) at java.net.URLClassLoader.access$100(URLClassLoader.java:71) at java.net.URLClassLoader$1.run(URLClassLoader.java:361) at java.net.URLClassLoader$1.run(URLClassLoader.java:355) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:354) at java.lang.ClassLoader.loadClass(ClassLoader.java:423) at java.lang.ClassLoader.loadClass(ClassLoader.java:356) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:264) at SDKMain.main(SDKMain.java:127) ] stdout[

] UnityEditor.Android.Command.Run (System.Diagnostics.ProcessStartInfo psi, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg) UnityEditor.Android.AndroidSDKTools.RunCommandInternal (System.String javaExe, System.String sdkToolsDir, System.String[] sdkToolCommand, Int32 memoryMB, System.String workingdir, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg) UnityEditor.Android.AndroidSDKTools.RunCommandSafe (System.String javaExe, System.String sdkToolsDir, System.String[] sdkToolCommand, Int32 memoryMB, System.String workingdir, UnityEditor.Android.WaitingForProcessToExit waitingForProcessToExit, System.String errorMsg) UnityEditor.HostView:OnGUI()