This option is unavailable in Canary Mail. The only way to change your password is via the web interface of your email provider.
Below mentioned are the directions on how to change the password for some of the email providers:
After changing the password, Canary will ask you to update the server settings.
You can do this via Canary > Settings > Accounts > Select the Account > Server Settings > Update the credentials. This can be done on all devices.