you should use anchors for this
The anchors feature is simple to use and is very effective with implementing flexible layouts. By default the views position is relative to the top left corner. There is nothing special about this corner and there is no real reason for all views to be position based on the distance from this...
but may be you are using them and may be for some other reason they are not working, if that is so you can use the mainform.rootpane resize event. (if you are in the mainform of course)
if my memory doesnt fail it is this one:
private Sub mainform_Resize (Width As Double, Height As Double)
End Sub