Assuming you're in Word 2007, to delete entries one at a time you can use

Insert=>Quick Parts=>Building Blocks Organizer

then click on the 'Gallery' column title and
scroll down to the items listed as being in the

'Page Numbers' galleries (there are several
  Page Numbers, Page Numbers(Bottom of Page),
  Page Numbers(Margins), Page Numbers(Top of Page))

and delete the ones  you don't want, or move them to another attached template (Alt, T, I) then detach the template.

You can also get to the organizer by using Insert=>Page Numbers and right click on a gallery entry and choose 'Organize and Delete'.
[The ones listed in the 'Current Position' section are the ones in the 'Page Numbers' of the four listed below.
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Hi

I would like to "clean" the page numbering design gallery cos
it have recorded all my test (e.g: 1/??)

Thx>>