First, I'll assume you are putting the page numbers in either your header or footer. Second, make sure that in each of your section headers or footers, your "same as previous option" is turned off. After you put in your page number (it will default to a 1, 2, 3 format), go to the section that you want the page numbering (first section?) as i, ii, ... and on your header/footer toolbar, click "format page number". this gives you the option of changing that section's page numbering to another format.
I'll assume too that you want the numbers that are 1, 2, 3 format to then start at 1 (I'll assume your first section is the one you want at i, ii.. and the next section is 1, 2, 3) go into that second section and choose format page number in that section the same way on your header/footer toolbar). You can choose to have those start at 1 on that same format option menu.