Yes. Every Leanpub book has a "Primary Author" who is essentially in the top position of control of a book.
A Primary Author can transfer their Primary Author status to another person who has a Leanpub account. A Primary Author can transfer this status by emailing us at firstname.lastname@example.org from the email address associated with their Leanpub account, and requesting that we transfer Primary Status to another Leanpub account.
The new person will need to indicate that they accept the transfer, and they will have to do so from the email address associated with their Leanpub account.
We would recommend you read our Terms of Service, particularly section 15, "Primary Authors and Co-Authors". Here is a link to our Terms of Service: https://leanpub.com/terms.