Hi Macroapa

The code below should do what you want, it will set the width and
height to 75% of the full screen size but you can change this to an %
you want.

Option Explicit
Dim oldHeight, oldWidth As Long
Dim newHeight, newWidth As Long

Private Sub CommandButton1_Click()

With Application

oldHeight = .Height
oldWidth = .Width

newHeight = oldHeight / 100 * 75
newWidth = oldWidth / 100 * 75

.WindowState = xlNormal

.Height = newHeight
.Width = newWidth

.Top = 0
.Left = oldWidth - newWidth - 3

End With

Hope this helps

Steve