ui.Window.SetText() is used to specify the window title. It requires a single argument of the character data type which is represents the new title does not return anything.
CALL wo.SetText("My Window")
Here is an example of a ui.Window object manipulation: a window is got by name and its title is changed:
MAIN
DEFINE wo ui.Window
OPEN WINDOW orders_w WITH 20 ROWS, 40 COLUMNS ATTRIBUTE(BORDER)
LET wo = ui.Window.forName("orders_w")
MENU "menu"
COMMAND "Change title"
CALL wo.setText("New window title")
COMMAND "Exit"
EXIT MENU
END MENU
CALL wo.Close()
END MAIN