1. Visit the official website of the British National Library.

2. Use the search function to enter keywords or related information of ancient books you are interested in.

3. Find the ancient book you want to download, click the link of the book and enter the detailed information page of the book.

Books can be downloaded for free. You can download them directly by clicking the download link. If there are access restrictions or payment requirements, you need to register an account and purchase access rights.