Seems to be a step missing here. There is a screw on the left hand side of the panel that needs to be removed to expose the RAM chips and hard drive.

I found it very straightforward to purchase a Kingston KC600 SSD drive, which includes an external caddy, then use the free Aomei cloning software to clone the existing drive, then follow this article to open up the Inspiron, remove the SATA drive and install the KC600 drive instead. Thanks! It had become unbearable slow running Windows 10 but now has another lease of life.