You have two options to remove a work sample from any collection:
Go to the collection, click on the work sample preview and select "Remove from collection" from the dropdown menu:
Go to the content item's details page and click on the "X" icon in the respective collection tag:
Good to know: Removing a work sample from a collection will not delete the item from your Authory account. It will still be in other collections and in your Content Archive. To fully delete an item, follow this guide.