For accessibility and best practice reasons, center aligning text or images has been removed from the WYSIWYG editor.
You can add a center aligned image to a column by using the Image block found within Blocks > Column Blocks > Replace Content. Column Blocks are then added to a row by going to the 'Column Options' drop down below the WYSIWYG editor.
Cascade Support Tutorials
For more information on what text options are available, please refer to the Cascade Support Tutorial on the WYSIWYG editor.
For more information on center aligning images, please refer to the Cascade Support Tutorial on the Image block.