You sure can.
In the thumbnail view of your zeeting, you'll unsurprisingly see a thumbnail of each slide, poll, video or other item of content in your zeeting. Look closer and you'll notice that in the top right-hand corner of each thumbnail there is a grey check box. To delete or reorder content, simply select the check box on the item/s you want to manage and you'll see a bunch of options including "Move to" and "Delete" appear across the top of the screen.
Another way to reorder your content is using drag and drop. Simply click on a thumbnail and drag it into the position you want. This method is only available on desktop.