OK, at least in principle, this shouldn't be difficult. Click the bullet character of the first item. That would highlight all bullets that are part of the same list (at that particular level). Then right-click again and select Adjust List Indents from the context menu. Specify the desired indentation. Repeat this for other bullets.
With a macro, you'd need something like this:
Code:
Sub ChangeListParasInDoc()
Dim LP As ListParagraphs
Dim p As Paragraph
Dim i As ListLevel
Set LP = ActiveDocument.ListParagraphs
For Each p In LP
For Each i In p.Range.ListFormat.ListTemplate.ListLevels
i.TrailingCharacter = wdTrailingTab
i.NumberPosition = 18 ' 0.25" indent from left margin
i.TextPosition = 36 ' position from left margin of text
i.TabPosition = 36 ' position of tab stop
Next i
Next p
End Sub