customising current email templates

1 - automation of forget my password / user is already there, i need it replaced it with mail chimp. 2 - automation of email when customer joins through newsletter or registered on our site. (Ryt now this is through mail chimp) is already there, i need it replaced it with mail chimp. 3 - automation of email to customers when they make a purchase and when their order is dispatched. (this is already there, i need it replaced it with mail chimp.) thanks.