1. Extract files from com_bfauction.zip

2. Copy entire contents of "admin" folder into /administrator/components/com_bfauction/
   (overwrite existing files).

3. Copy entire contents (except css folder if you've customised style) of
   "component" folder into /components/com_bfauction/
   (overwrite existing files).

4. Copy com_bfauction.xml into /administrator/components/com_bfauction/
   (overwrite existing file)