Limpiar un arreglo (array)

Dim readtext() As String = File.ReadAllLines("archivo.txt")
Array.Clear(readtext, 0, readtext.Length)

fuente: https://stackoverflow.com/questions/713867/what-is-the-best-way-to-clear-an-array-of-strings

ReDim readtext(0)

ReDim Preserve

Erase array fuente