Some times you will have to add a lot of diagrams and graphics to word documents for better understanding. There is a saying a picture worth thousand words. For these pictures you would add captions or figure tags with a reference number.
When you add new pictures or remove the existing one , you will end up the figure numbers been out of order.
Normally if you highlight the figure number and right click and select update field will update the figure to the correct sequence.
But if you have several hundreds of pages this is a tedious .
Following is a short cut.
1. Select the whole document (Press CTRL+A)
2. Press F9
This will update all fields automatically.
Note: this should work on the older versions of MS Word as well