Simple question I can't answer xD

[bergerkiller]

I bet the answer is very easy , maybe just one extra word, but:
How can you make a function/sub change the inputvalue?

As example:

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim testval As Integer = 1
        MsgBox("Before: " & testval)
        Testfunc(testval)
        MsgBox("After: " & testval)
    End Sub

    Public Overridable Function Testfunc(ByVal Testval As Integer)
        Testval = 2
    End Function

The after value should be "2", but at the moment it stays "1".

Hoping for a quick reply