For Bethany, the household handywoman, and Ruthy who enjoys working with tools:) Awesome website for homeowners: The Family Handyman. Anything that you need fixed, there's a step by step guide with difficulty rating and cost.
Solar Lights - DIY Quick Fix. Basically, there's a battery inside that charges the solar panel. Unscrew the head of the light and replace the battery. Will work unless the battery chamber has corroded.