You can see whether you have a HDD or SSD by opening Windows disk defragmenter (in Start menu, start typing "defrag" and the application name should appear for you to click on it). In the Optimize Drives window that appears, the column "Media Type" will state whether you have "Hard disk drive" or "Solid state drive". Here is what Dell's specifications say that your system supports:   Any M.2 PCIe drive will be faster than a SATA drive. You can choose any size, up to 4 TB. You are not limited to the sizes listed in the specifications, as those are just what Dell tested several years ago when the laptop was designed. Follow the disassembly and reassembly steps in Dell's Service Manual.Look on YouTube for videos showing disassembly of your model. But, be cautious with them, as some use steps or methods that are not appropriate. Use the videos to add to your understanding of what to do, but follow the steps in Dell's manual. Whenever touching components or working inside a computer, wear a grounded wrist strap, also called anti-static wrist strap, ESD wrist strap, or ground bracelet. It's a cheap and sensible precaution. Rest the laptop on an anti-static mat or at least a reasonable alternative such as corrugated cardboard.
Does anyone know if my Dell Inspiron 5570 laptop has a HDD?  My C drive is almost full (my C drive only has storage space of 223GB) I want to increase my storage space to either 1TB or 2TB.  However I have no idea what to buy.  Any help would be much appreciated.  
Dell Inspiron 5570 Hard Drive