If you want to rename a character in your script got to Edit > Rename Character:
To change a character's name throughout the script, choose it from the Character to Rename dropdown menu...
...and type the new name into the Rename To field:
After the new name has been entered, click Rename.
The program will scan the entire document and change every instance of that name. Note that the character name will be replaced in all elements (i.e. Action, Parentheticals, Alt Dialogues, etc.). The name will also be changed in all tools (i.e. SmartType, the Characters section of the Navigator, Reports, etc.).