You can delete Products from your SI 2017 Catalog individually or you can delete multiple Products at one time using the Delete button. You can select multiple Products in the grid by holding down Shift (to select a series) or Ctrl (to select outside of a series).
You can also right-click to delete, or use the keyboard shortcut Ctrl+Del.
Deleting a Manufacturer will delete all Products from your Catalog assigned to the Manufacturer.
Deleting a Category will delete all Products from your Catalog assigned to the Category.
There is no "undo" in SI 2017. Once deleted, there is no recovering these Products unless you restore a backup of your SI 2017 server.