Click the selection tool 
in the tool bar at the top of the editor window.
Select the text objects you want to change.
To select one text object, click it. To select a subset of the text objects, click outside of any object and drag across the text objects you wish to select. Alternatively, click each text object while holding down the Shift key. To select all text objects at once, choose Select All from the Edit menu at the top of the editor window. Handles (small black boxes) will appear to indicate that the text objects are selected.
Click the left, center or right justification button as pictured below.
