Rebranding in the simple sense is the creation of a new name or design or the combination of both to have a distinct/differentiated positioning in the market. Changes in brand logo or brand name will help to polish the tarnished image of the brand, gain competitor advantage, and to generate some fresh energy for increased promotion. Sometimes brands look for a slight change in brand logo, rather than attempting a complete change. CEAT Tyres, Godrej, etc are examples of brands that adapted rebranding strategy for increased promotion.
Read this interesting article on Rebranding: Looking behind logos in India