I need to delete something from a .txt file but it leaves an empty line! I have set code to stop this but it deletes something else

I need to delete something from a .txt file but it leaves an empty line! I
have set code to stop this but it deletes something else

I need to set this piece of code in vb so that a user can delete a
specific string from a .txt document. But when they do, it leaves an empty
line. I then got more code to stop this but then it deletes something else
within the file with the empty line.
Code:
If (txtDelUser.Text = "admin" Or txtDelUser.Text = "guest") Then
rtbOutput2.Text = "You tried to delete: " + txtDelUser.Text + ".
But the user is protected by default."
Else
Dim ln As Integer = 1
rtbOutput.Text.First(Of Text = Text.CopyTo.ClipBoard
'Removes the selected username from list of usernames
Dim lines As New List(Of String)
Using sr As New StreamReader("C:\ProgramData\Hax Client\User
Data\All Usernames.txt")
While Not sr.EndOfStream
lines.Add(sr.ReadLine)
End While
End Using
For Each line As String In lines
If line.Contains(txtDelUser.Text) Then
lines.Remove(line)
Exit For 'must exit as we changed the iteration
End If
Next
'End of removing the line
Dim fs As New FileStream("C:\ProgramData\Hax Client\User Data\All
Usernames.txt", FileMode.Append)
Dim sw As New StreamWriter(fs)
Dim foundBlank As Boolean
For Each line As String In lines
If line.Length > 0 Then
sw.WriteLine(line)
' Reset blank line flag
foundBlank = False
Else
If Not foundBlank Then
' Blank line: write first one
sw.WriteLine(line)
' Set flag to indicate that blank line was found
foundBlank = True
End If
End If
Next
sw.Close()
fs.Close()
My.Computer.FileSystem.FileExists("C:\ProgramData\Hax Client\User
Data\" + txtDelUser.Text)
My.Computer.FileSystem.DeleteFile("C:\ProgramData\Hax Client\User
Data\" + txtDelUser.Text + ".txt")
rtbOutput2.Text = "Deleted user: " + txtDelUser.Text
End If
Text file:
admin
guest
testing
Can you either look over my code or give me some code that will allow me
to delete from the .txt file, by whats entered into a textbox, without
leaving an empty or a way to get rid of the empty line.
Thanks!