[Koha] how to delete a record?

Dear All; I am part of this support group and have asked before how can I delete a whole entry, this is, a bibliographic record. I went to the address supplied for a Koha manual, but the item "delete biblio record", had not been developed yet. So I have to bother you. We do not use yet a marc record, as we have our own classification system in a small library of about 7000 books. I need to do some deselection, and need to delete some titles, and/ or some second copies. How is this done? I have asked Chris last year if after doing this I could use that"barcode" number again. He said it should be possible, but I have no idea how to do it. Many thanks for your answer. Silvia Soto-Bussard Librarian Theosophical Society Wellington