These actions can be taken in the presentation editor. From your dashboard, just click on the presentation and then Edit.
To reorder slides, use the Sidebar on the left-hand side of the screen and just drag and drop to reorganize.
To find more options about a slide, look for the arrow next to each one and click on it to find the Duplicate and Delete options.
You'll also be able to Insert new slides, before and after the selected one.
Please be mindful when deleting a slide, since this action can't be undone 🚫