Hi Steven,
Do you mean that you want to know the answers for the question two questions?
1. Remove unwanted/unused/disabled mailboxes
2. Convert some user mailboxes to shared mailboxes (info, sales, etc) due to license.
If yes, I will answer the questions for you.
A1. After deleting the users, the corresponding mailboxes also will be deleted. For more detailed information about how to delete users, you can refer to the link below: https://support.office.com/en-nz/article/Delete-or-restore-users-d5155593-3bac-4d8d-9d8b-f4513a81479e
A2. About how to convert a mailbox, you can refer to the link below: https://technet.microsoft.com/en-us/library/jj710164(v=exchg.150).aspx
Best Regards,
Anna