In order to perform this task you will need to remove all of your Media from your Public collection and ensure that none of your Collections are being shared with the Public group.
In order to remove your videos from the Public collection, log into your Admin Dashboard.
Next, click on "Public" in your Collections list.
Drag all the Media from the Public collection into another collection. To do this highlight all of the Media in your public Collection and drag it over to another Collection. If you want to distribute the Media into a few different Collections then move the Media items one by one into the Collections of your choice.
To ensure that none of your Collections are being shared with the Public group we recommend opening your site settings menu and navigating to the Groups pane.
In the Groups pane click on View next to the Public group.
This will bring up a list of all the Collections you are sharing with your public Group. To remove the public Group from each one of these Collections click on the link to each Collection one by one.
Clicking on the link to the Collection will open up that Collection in the Admin Panel's library.
From here, click on Manage in the right hand column next to "Shared with". A window will pop up displaying the members of your Group. Click on the X next to the Public Collection and click OK in the pop up box to delete this membership.
Repeat this step with all of the Collections in the Public Group.