If you reside in the US and are the registered owner of the computer, a disc containing the factory-installed operating system specific to your system, can be requested from HERE.
Note: Dell may charge for the disc.
You should rethink your plan. Nowadays all that is required is to uninstall anything you don't want. The disk has been prepared using a disk image, not separate installations of Windows, programs and utilities as in the past. You will lose all factory installed tweaks that don't have disks. MS Office Starter for instance is Word and excel in limited editions that don't expire. For many home users, that is all you need to read and write Word files and simple excel files. Don't change anything until you use the computer and make sure all is working fine. Also check the formatting of the disk. Many new computers have small C partitions for the system files and an empty D partition for installing all your files, photos, videos and new programs. Do some research before you do anything.