How do I change the invitation mail sent to new users?

To customize the email sent to invited users:
1) Enable Email Customization from Settings → Add-ons → Email Templates.
2) From the same setting, click the link ‘Configure Email Templates’. It’ll take you to the email template listing.
3) Hit the ‘Add Email Template’ button.
4) On the new template form, in ‘Template Type’ dropdown choose ’Member Invitation’.
5) Use placeholders to have data like ‘Recipient Name’, ‘Confirmation Link’, etc.
6) Hit the ‘Create Email Template’ button. You’ll be taken to the preview. Activate this template from the ‘Activate’ button on top right.
And you are good to go.