Six Sigma = Total Quality Management (TQM) minus weaknesses of Total Quality Management (TQM).
In TQM philosophy, any project is ok as long as it improves Quality. Six Sigma methodology is a more holistic approach which is based on facts, is data driven, is result oriented and exhibits a strong linkage to strategic goals. It can also be applied to all common business processes like Administration, Research & Development, Sales & Marketing, etc. If you know Quality Management, you’ll easily learn Lean Six Sigma.