You’re able to remove yourself as a user from multiple sites using the Bulk Actions drop-down menu on your My Sites page.

Select the sites you want to be removed from by clicking on the check-mark next to their site title (their site title header changes to blue when selected), select ‘Remove me from selected sites‘ from the ‘Bulk actions’ drop-down menu and then click Apply.

You’ll only see the option to select a site if you are assigned the role of an administrator or teacher.
This automatically removes you as a user from the sites and remove the sites from your My Sites page.
Remove from Student Blogs
You remove yourself from student blogs attached to a class blog via My Class using My Class > Student blogs.

Select the student blogs you want to remove from class by clicking on the check-mark next to their site title (their site title header changes to blue when selected), select “Remove from class‘ from the ‘Bulk actions’ drop-down menu and then click Apply.

This removes their blogs from your Student Blogs page and removes you as a user from their student blogs.