Change password code in asp.net with vb

Question

hey all..i want change password code in asp.net with vb..
i wrote following code..but the thing is that the user can enter any email id or password and update it.


Protected Sub ImageButton1_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton1.Click




        Dim cn As New SqlClient.SqlConnection(cnstring)
        Dim cmd As New SqlClient.SqlCommand
        Dim sql As String
        Dim vname, vpswd, vnew, vid As String
        Try
            vname = TextName.Text
            vpswd = TextOPswrd.Text
            vnew = TextNew.Text
            vid = TextEID.Text


            sql = "update Reg set Pswrd=@Pswrd where EID=@EID"
            cn.Open()
            cmd.CommandType = CommandType.Text
            cmd.CommandText = sql
            cmd.Connection = cn
            cmd.Parameters.AddWithValue("@EID", vid)
            cmd.Parameters.AddWithValue("@Pswrd", vnew)
            cmd.ExecuteNonQuery()
            Literal1.Text = "<b>Your password has been changed successfully</b>"
            cn.Close()
        Catch ex As Exception
            Literal1.Text = ex.ToString
        End Try


    End Sub