What could be the ways to extend life cycle of a product which has generated good business for years,has started now losing way before competition?

First you should to look for the product growth in the market if there is no growth then it is better to drop the product but if there growth then you should focus on the actual and augmented product through which you could improve value to the customer. 

Do competitor analysis and find what your competitors doing and then try to be better than the competitor.

Depends the product, but can do several things... for example you can change some detailed characteristics of the product, the package, the distribution channel, the consummers niche, the market globalization, and so on.

But be carefull, a product in end life cycle can be a budget sucker; and maybe you can launch new products with inferior costs. 

Other way, if that is yours "umbrella´s" product, invest on it and make changes.