Serial data overwrite on visual basic - vb.net

Question

I am new to visual basic . I am sending data from arduino evey 1s say current. I wanted to print on text box. Here is my code on VB side . Problem i am facing here . I am getting data but Not ovwrwriting .it just print one after the other. I am using VB2010.
VB code
Imports System
Imports System.ComponentModel
Imports System.Threading
Imports System.IO.Ports
Public Class frmMain
Dim myPort As Array 'COM Ports detected on the system will be stored here
Delegate Sub SetTextCallback(ByVal [text] As String) 'Added to prevent threading errors during receiveing of data
Private Sub frmMain_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
myPort = IO.Ports.SerialPort.GetPortNames() 'Get all com ports available
cmbBaud.Items.Add(9600) 'Populate the cmbBaud Combo box to common baud rates used
cmbBaud.Items.Add(19200)
cmbBaud.Items.Add(38400)
cmbBaud.Items.Add(57600)
cmbBaud.Items.Add(115200)
For i = 0 To UBound(myPort)
cmbPort.Items.Add(myPort(i))
Next
cmbPort.Text = cmbPort.Items.Item(0) 'Set cmbPort text to the first COM port detected
cmbBaud.Text = cmbBaud.Items.Item(0) 'Set cmbBaud text to the first Baud rate on the list
'SerialPort1.PortName = cmbPort.Text()
'SerialPort1.BaudRate = cmbBaud.Text()
btnDisconnect.Enabled = False 'Initially Disconnect Button is Disabled
End Sub
Private Sub btnConnect_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnConnect.Click
SerialPort1.PortName = cmbPort.Text()
'Set SerialPort1 to the selected COM port at startup
SerialPort1.BaudRate = cmbBaud.Text()
'Set Baud rate to the selected value on
'Other Serial Port Property
SerialPort1.Parity = IO.Ports.Parity.None
SerialPort1.StopBits = IO.Ports.StopBits.One
SerialPort1.DataBits = 8 'Open our serial port
SerialPort1.Open()
btnConnect.Enabled = False 'Disable Connect button
btnDisconnect.Enabled = True 'and Enable Disconnect button
End Sub
Private Sub btnDisconnect_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnDisconnect.Click
SerialPort1.Close() 'Close our Serial Port
btnConnect.Enabled = True
btnDisconnect.Enabled = False
End Sub
Private Sub btnSend_Click_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSend.Click
SerialPort1.Write(txtTransmit.Text & vbCr) 'The text contained in the txtText will be sent to the serial port as ascii
'plus the carriage return (Enter Key) the carriage return can be ommitted if the other end doe
End Sub
Private Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort1.DataReceived
ReceivedText(SerialPort1.ReadExisting()) 'Automatically called every time a data is received at the serialPort
End Sub
Private Sub ReceivedText(ByVal [text] As String)
'compares the ID of the creating Thread to the ID of the calling Thread
If Me.Current_Read.InvokeRequired Then
Dim x As New SetTextCallback(AddressOf ReceivedText)
Me.Invoke(x, New Object() {(text)})
Else
Me.Current_Read.Text &= [text]
End If
End Sub
Private Sub cmbPort_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
If SerialPort1.IsOpen = False Then
SerialPort1.PortName = cmbPort.Text 'pop a message box to user if he is changing ports
Else 'without disconnecting first.
MsgBox("Valid only if port is Closed", vbCritical)
End If
End Sub
Private Sub cmbBaud_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
If SerialPort1.IsOpen = False Then
SerialPort1.BaudRate = cmbBaud.Text 'pop a message box to user if he is changing baud rate
Else 'without disconnecting first.
MsgBox("Valid only if port is Closed", vbCritical)
End If
End Sub
Private Sub RELAY_ON_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RELAY_ON.Click
SerialPort1.Write("1")
End Sub
Private Sub RELAY_OFF_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RELAY_OFF.Click
SerialPort1.Write("0")
End Sub
End Class
Arduino Code.
float Output_Current ;
void TakeReading()
{
newaverage = analogRead(A5);
Output_Current = 0.0336666666667*newaverage - 17.17;
}
void loop()
{
Serial.println( Output_Current );
delay(1000);
}