When you make something young again or give it more life and energy, you rejuvenate it. For example, you can often rejuvenate a not-quite-dead plant, bringing it back to health with some water and some TLC.
One way to remember the word rejuvenate is to pick it apart to its heart, the juve. This juve sounds like juvenile — which refers to youth. Add the prefix re, which means "again," and the "ate" suffix, which stands for "do or make." Put them all together and you get "make young again" — the meaning of rejuvenate. We all want to be younger, as witnessed by all the ads for products that promise to rejuvenate us through special cosmetics or foods or exercise equipment.