My three year old Inspiron 7737 running Windows10 Home has ground to a halt mainly because of 50-100% ST1000LM014-1EJ164 disk utilisation. I was thinking about replacing this disk with a 500GB SSD however I do not have my original Windows8 media and associated license key (and this would need to be upgraded to Windows10 which I achieved free of charge). I currently have  643GB free of 913GB so this would be feasible if this could be achieved ideally without the need to purchase a Microsoft license and installing from scratch. 

Is there a cost effective way of speeding up my laptop using my current licensed Windows10 OS?

Thanks in anticipation.