exporting next image from listbox - vb.net

Question

I am trying to build an ImageConverter for my cousin (he needs that for his job) to export images in the following formats : 1. 2500x2500 , 2.1500x1500 and 3.800x800.
I only managed to export only one picture at a time in this formats , but he usually has over 50 pictures to convert in this formats daily , so I added a listbox so he can drag and drop his images in the listbox .I did managed that , but I don't know how to export the pictures that are loaded in the listbox , it needs to export one by one . The code I am using to export the images with "Export button" is here :
If (Not System.IO.Directory.Exists("C:\Users\Administrator\Desktop\" + KryptonTextBox1.Text)) Then
System.IO.Directory.CreateDirectory("C:\Users\Administrator\Desktop\" + KryptonTextBox1.Text)
Dim picturepath As String
picturepath = "C:\Users\Administrator\Desktop\" + KryptonTextBox1.Text
pathtxt.Text = picturepath
End If
Dim fileName As String = KryptonListBox1.SelectedItem.ToString()
Dim pathname As String = OpenFileDialog1.FileName
picturename = Path.GetFileNameWithoutExtension(fileName)
BildNametxt.Text = picturename
'converting picture in 2500x2500 format
Try
If (Not System.IO.Directory.Exists(pathtxt.Text + "\Amazon")) Then
System.IO.Directory.CreateDirectory(pathtxt.Text + "\Amazon")
Else
PictureBox2500.BackgroundImage.Save(pathtxt.Text + "\Amazon" + "\" + picturename + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg)
End If
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
Try
If (Not System.IO.Directory.Exists(pathtxt.Text + "\1500")) Then
System.IO.Directory.CreateDirectory(pathtxt.Text + "\1500")
Else
PictureBox1500.BackgroundImage.Save(pathtxt.Text + "\1500" + "\" + picturename + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg)
End If
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
Try
If (Not System.IO.Directory.Exists(pathtxt.Text + "\800")) Then
System.IO.Directory.CreateDirectory(pathtxt.Text + "\800")
Else
PictureBox800.BackgroundImage.Save(pathtxt.Text + "\800" + "\" + picturename + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg)
End If
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
MessageBox.Show("Images succesfully converted!")
resizedimage2500.Dispose()
resizedimage1500.Dispose()
resizedimage800.Dispose()
So how can I do the same thing with the loaded listbox ? Any help is apreciated ! Thanks in advance