For an individual admin user you need to log in and go to Admin > Users and then find your account. Then click on the  link.
You should now ensure that 'Receives alerts:' is not ticked, see figure 1.
Figure 1 - Receives alerts
To turn off email notifications globally (i.e. for all users/admins), we have introduced a new feature in version 3.667 of the software.
To disable email templates you will need to select the appropriate email template and click on the  link. You will then see an 'Enabled?' tick box, see figure 2. Once un-ticked and saved, this will stop the email template from sending any emails.
Figure 2 - Edit email templates
You can also optionally choose to 'hide' these emails from the list visible from: Admin > Content > Email templates. Click on the [hide] link to do this (see figure 3). Note, you can later add such hidden emails back into this list via the 'View hidden templates>>' link at the bottom of this page.
Figure 3 - Manage content area