You can use  one M.2 NVMe drive and  one 2.5" drive - hard drive or SSD.  However, if the system was purchased without the 2.5" drive, you'll also need a bracket, cable and screws to mount the drive - which will be Dell-specific parts.  Contact Dell Spare parts for those (in the US, 1-877-717-3355).  A 4T SSD or a 2T hard drive will work (choose the latter carefully;  many are Seagates, and their current notebook drives are sorely lacking in the reliability department). The system will support 2x8=16 G RAM, but if your current RAM runs at 2400, so will the new RAM even if it is capable of 2666.  The RAM speed is controlled by the CPU -- which isn't upgradeable.  
Hi. I have read some threads here about upgrades for this model but still confused. My laptop comes with PCIe SSD 256 GB and I want to upgrade to 1x2TB 2.5-inch HDD and 1x512GB PCIe SSD. Is it possible? I bought it in 2019 but I don't know its generation. I also have a question about Crucial SSD. In this link: [URL] It claims that those SSDs on the list support Inspiron 15 (5570) but there is a 4-TB SSD present in the list. So I am not sure if I can upgrade to 4-TB or not because some threads here say that 2-TB is the maximum this model can have. Also, can I replace the original 1x2400MHz 8GB RAM with 2x 2666MHz 16GB RAM? Thanks so much.
Dell Inspiron 15 5570 Upgrades.