From LSWiki

Renew is the ability to burn your injuries away with fire. This is a strong personal heal effect, but if activated in combat, it is also a powerful area attack that deals fire damage. It costs 50 points of elemental fire resource energy, fueled by the Convert charm; this translates to around 250-300 spell points, with adequate skills. The damage only hits enemies that you are fighting with, and does not hit your familiar or other followers.

Important note: you must be damaged to activate this charm. Apparently, the more damaged you are, the more damage the charm can do.

Your familiar must be alive and present in your environment for this charm to work.

Usage

concentrate on renewing myself