In this video I go over your options on as far as what you can use to remove and replace a rounded off bolt or nut.

Pittsburgh Bolt Extractor Metric: http://amzn.to/2aRGuSZ
Pittsburgh Bolt Extractor SAE: http://amzn.to/2bneNBb
Awesome Impact Bolt Extractor Kit Here: http://amzn.to/2aRFMoT
Locking Vise Grips: http://amzn.to/2aRFUo9