To change the numbering style for a page number or to specify a number to use as the first page number, should be clicked in the page number button in the header & footer group on the header & footer tools design tab.

Format Page Number

Explanation:

In order to change the numbering style for  page number or to choose the numbering position or to specify the number to begin with, following the following steps:

a. Go to Insert tab

b. Go to Header & Footer section

c. Click the dropdown icon beside Page Number

d. Select Format Page Number.