I was able to upgrade to a 2TB SSD using a Samsung 860 EVO 2TB M.2 SATA Internal SSD. Note that this is a V-NAND SSD with an 'M' & 'B' Key SSD Edge Connector. This is critical when you order the replacement drive. If you get the right drive connection, it is easy to upgrade. I didn't see much speed improvement, but I now have the extra disk space I need.
As others have pointed out, the memory is permanently mounted on the motherboard, so you can't upgrade.