Deleteion of any file is simply:
Code:
if FlieExists(FileName) then
  DeleteFile(FileName);
As for validation, you can achieve it on two levels. For example if your using a standard Edit control (TEdit) then in its OnKeyPress event you can place code to trap and kill invalid characters:
Code:
procedure NameKeyPress(Sender:TObject; var Key:Char);
begin
  if not (Key in ['A'..'Z','a'..'z']) then // check for anything but a-z
    Key := #0; // This kills the key stroke
end;
Take a read through the Delphi help files, and on some basic UI tutorials. Theirs lots of infomraiton out their on this type of stuff. A good resource is Tamaracka.com