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Hi Sunil
Anthony is right. Changes to your data should be automatically reflected to your service. Anyway what you can do is publish .mxd which references the data in SDE using a python script. You can run the overwrite map service py script.
Refer this url:
http://resources.arcgis.com/en/help/main/10.1/index.html#//00540000001r000000
You can automate the running of this script in every 2 hours using windows task scheduler.