When you have created a lettering object, you can select it and make changes to it interactively or by adjusting object properties.
Click Lettering and then click inside the lettering object. An I-beam appears.
Edit the text as required. The lettering shows its wireframe.
Press Shift+Enter to start a new line. Press Enter to complete.
Alternatively, double-click the lettering object. The Object Properties > Special > Lettering docker opens.
Edit the text in the text entry panel and make any other adjustments you require.
Click the Update Text button.