Here is a short video that will take you through this process:

To delete a layer on the scene or project timeline, you can right-click on it and choose the Delete option.

An alternative method is you can select the element, then either press the wastebasket 🗑 icon above, or the Delete key on your keyboard to delete it.

If you see an element whose layer is locked, you will need to unlock it first by clicking on the lock 🔒 icon beside it to edit it.