Changing the default confirmation and unsubscribe messages

Hello,

I want to customize the default text for the unsubscribe page. I found this page in the Mailpoet knowledge base on how to change those:

http://support.mailpoet.com/knowledgebase/customize-your-confirmation-pages/

But it seems that I cannot find those options anywhere. I suppose that it’s changed with an update. Where can I find these options now to change these messages? Thank you in advance!

https://wordpress.org/plugins/wysija-newsletters/