Ok, I found that... it's what I need. Thank you :-)

Option Explicit
Function Main()
' Declare Variables
Dim oPKG
Dim oConnection
' Get Package Object
Set oPKG = DTSGlobalVariables.Parent
' Get Named Connection
Set oConnection = oPKG.Connections("Text File (Source)")
' Set Filename to new value
oConnection.DataSource = "X:\YourPath\YourFile.txt"
Set oConnection = Nothing
Set oPKG = Nothing

Main = DTSTaskExecResult_Success
End Function