To delete a specific node, select the node on your canvas. In the panel on the right, in the top right corner, select the 'bin' icon. This will remove the node and all subsequent nodes that was connected to it from your flow. This action cannot be undone.
Once you've selected a flow, a number appears in brackets next to the 'bin' icon at the bottom of your list of flows. This indicates the number of nodes that were deleted from this flow. Clicking on the bin icon brings up a panel that displays all the nodes that were deleted from the selected flow.
To restore these nodes (and their children nodes), you have to refer to the node in the logic section of another node currently forming part of your flow. Once you save this node, your deleted node and all the subsequent nodes that were connected to it before, will be restored to your flow and removed from the 'deleted' panel.