Thanks for reaching out to us. If someone has shared a prezi with you, hover over a thumbnail and click on the icon to the right of Edit.
Then find your name on the list, click on the drop-down menu, and select Remove from Prezi.
If you’d like more information, you can read more about unsharing a prezi here: http://bit.ly/1n5PjsP. Hope that helps! If you have any more questions, don’t hesitate to ask!