You can go to format and in grand total section there is a "Label" text box at bottom of format section to change the alias name.
Thanks a lot.
Hello Winson Lui,
Please right click on "Grand total", then "Format".
Finally, check the bottom space "Label".
Here, you will be able to hange the label to Overall.
Hope this helps!
Edit: Oh well, three replies! Congrats!
Responsive and really helpful.