How do download current Windows 10 operating system

A number of years ago I purchased a Del Inspiron 3531 laptop with Windows 8 from QVC. Soon after I upgraded to Windows 10.  The laptop came preloaded and they did not provided and CDs with the operating system.  It required the minimum of setup & installation.  I now find myself in the position that I believe that I need to reload the operating system (I assume Windows 10).  Is this available for download?  Are there any cautions anyone may provide?  I have backed-up most of my data.  So, I'm not too concerned about backup.  I'd appreciate any assistance you can provide.