Ivan, I wouldn’t change the way you write at all. That’s your voice and that’s what attracts your readers.
Instead, I would fix your sign-up form. This is probably where you’re losing people. I checked it out. It just says ‘free ebook’ Instead I’d tell the reader what she’s getting. Tells us what genre you write in. Maybe one sentence for what the book is about.
The landing page/sign-up form is everything with email. Think of the form through the reader’s eyes. How can you make your free book offer so enticing they can’t help but sign up.
I would remove the frequency choices from the sign-up form. I’d add that choice once they subscribe. Show that too early and you’ll turn people away.
Here’s mine if you’d like an example: