The Choose Via Sizes dialog is used to custom define Via hole and diameter sizes.
The dialog is accessed by pressing Shift+V while interactively routing (Route » Interactive Routing).
Select a Via in the left-hand pane of the dialog to view and edit the sizes for that Via. When you select a Via, the right side of the dialog displays information for the selected Via.
Simple(Via hole size and diameter are the same through all layers),
Top-Middle-Bottom(different Hole Size and Diameters can be set at Top Layer, Middle Layer and Bottom Layer), or
Full Stack(different Hole Size and Diameters can be edited at each layer, including all signal layers and planes).
Full Stack, you will need to individually enter a diameter for each available layer.