Changing the grid size in Allegro PCB Editor

Hi,

      All of our projects are been put in (mm) dimensions only.In PCB Editor me had kept the grid size as 2.54(mm) initially. Then after some referred on line books i divide the value by 2 (i.e).,2.54/2=1.27(mm). If i kept this means i have to zoom the components by too inner.Its create me put the manual routing problem in editor.

So can provide the solution that what is grid size want to kept in editor.