It seems that many people are concerned about the voice and accent training and their communication skills. Yes, there are institutes available for this, but, better look for a good book available in market. You also need to listen to CNN, Star News, English movies (without watching and just listening to the content), practising the accent in front of mirror.
You also need to serach for websites available on the subject. One such site is http://www.americanaccent.com.
All this helps getting a good accent. If possible, try to talk to a native and ask him/ her to correct you. This is not an easy task and all this takes at least 3-6 months to grasp and learn.
Be Patient! Best of Luck!