Managing your download settings
Go to Shelf > Loans > Actions > Choose Download Behavior to change your download settings.
"Automatically download" setting
The "Automatically download" setting controls whether titles are downloaded automatically right after you borrow them. You can choose Everything, Titles under..., or Nothing.
Choose Titles under... to automatically download smaller titles (usually books) but exclude larger ones (like graphic novels and audiobooks).
Tap the underlined 20 megabytes (mb) to adjust the title size you'd like automatically downloaded. Most books are under 20 mb, many graphic novels are more than 100 mb, and most audiobooks are more than 300 mb.
"Download only on Wi-Fi" setting
The "Download only on Wi-Fi" setting prevents loans from downloading on a cellular data connection.