You can edit a symbol by changing the symbol’s artwork or you can redefine the symbol by replacing it with new artwork. Editing and redefining a symbol changes the appearance of the symbol in the Symbols panel, as well as all instances of the symbol on the artboard.
Select an instance of the symbol and click Edit Symbol in the Control panel. When the Alert box opens, click OK.
Double-click an instance of the symbol. When the Alert box opens, click OK.
Double-click a symbol in the Symbols panel. A temporary instance of the symbol appears in the center of the artboard.