delete an item of a list(of..)

[gispe]

Hi!
im startin programmin in vb.net.
in the program im doin now, im workin with a global variable 'public library as new biblioteca' that has should be a list of books that user wants to load.
thing is that when i try to delete a book, i have to check if the code entered in textbox1 maches with the codes that the library has.
to search in the library im using: "library.Contenido.Item" but its givin me this error: "'Argument not specified for parameter 'index' of Public Default Property Item(index as Integer as T)", but dont know how to correct it :(
here is the class to delete the book:

Public Class Bajas

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim i As Int32
        Dim total As Int32

        If (TextBox1.Text < 1000) Or (TextBox1.Text > 32000) Then 'valida q se ingrese codigo bien
            MessageBox.Show(" Ingresar codigo correcto. de 1000 a 32000")
        Else
            For i = library.Contenido.Count To 0 Step -1 'esto recorre todo lo que haya cargado en el list of 
                If (library.Contenido.Item = TextBox1.Text) Then
                    'Argument not specified for parameter 'index' of Public Default Property Item(index as Integer as T) 
                End If
            Next
        End If
    End Sub
End Class

thanks!!