In regards to your other reply to my previous post about including a
user option to select the font size as well as the font name.
Just use the same form. Add another Option Group with the possible
Font sizes. Code the Report Open event as follows:

DoCmd.OpenForm "OptionFormName", , , , , acDialog
Dim TheFont as String
Dim intSize as Integer
Select Case forms!OptionFormName!FontNameOptionGroupName
Case is = 1
    TheFont = "Arial"
Case  is = 2
    TheFont = "Times New Roman"
Case is =  3
    TheFont = "Nuptial BT"
Case Else
    TheFont = "Script MT Bold"
End Select

Select Case forms!OptionFormName!FontSizeOptionGroupName
    Case is = 1
        intSize = 10
    Case is = 2
        intSize = 12
    Case else
        intSize = 8
End select

Dim c as control
For each c in Me.Section(0).Controls   
    If TypeOf c is TextBox Then
        c.FontName = TheFont
        c.FontSize = intSize
    End If
Next

I have no idea, however, what you mean by 'Label size' in this post.
Do you mean the Avery Label sheet number, i.e. 8160 to 8213?
It would be easier to simply create a second label report, and using
another option group, open that report rather than this one, as it's
not simply changing the size of the label, but also their horizontal
placement and the size of the detail section.

Do you mean to alter the height of a label control at runtime?
Not really recommended for mailing labels, as the size of the paper
label is fixed.
But you can experiment, if you wish.
The above is using Text controls, not label controls.
You could add another Option Group to the form.
Use another Select Case, similar to the  above.

Dim intHeight as Integer
Select Case forms!etc. as above
    Case is = 1
        intHeight = Int(0.33 * 1440)
    Case is = 2
        IntHeight = Int(0.5 * 1440)
    etc.
End Select               
   
Then add to the coding as above:

c.Height = intHeight

The measurement is in twips, 1440 per inch, so a 1/2-inch height would
be = int(0.5 * 1440)