Naming a sheet
In the sheet preview panel, hover over the sheet you would like to change the name of, then click inside the title box. You should be able to change the title of the sheet once you see the blinking cursor.
After changing the name of your sheet, don’t forget to save your diagram to confirm the changes.
Changing the order of sheets
In the sheets preview panel, select the sheet you would like to change the order of, then drag it up or down the panel to its target destination.
Information on naming sheets or diagrams on Editor versions before 6/27/18: https://support.cacoo.com/hc/en-us/articles/207282727-Naming-a-sheet-or-diagram