The procedure to update your database with EOD files depends on the source of the EOD file (from where you downloaded it), type of file (Text file or CSV file or Metastock file) and the structure of the File (how the data is arranged in the file (What is in each column of the file). If you can give these details or post a copy or part of your EOD file, I can give the procedure.
Please note: If you are using Trial version of AmiBroker, you can not update your database.
-Anant