Mouse: Click the text with the Type tool
To edit a type layer, you usually double-click the name of the layer in the Layers palette. However, you can also open the Type dialog box for a given type layer by using the Type tool. If you click a transparent area with the Type tool, the Type dialog box opens, and whatever you type is placed on a new layer. If you click the actual type in the layer, the Type dialog box opens with that specific text in it so that you can edit the existing type layer.