Can I upgrade the memory on late 2013 Retina MacBook Pro?
The RAM is soldered on so it is not upgradeable.

The SSD CAN be upgraded, with a standard PCIe M.2 drive if you buy an internal adapter ($2-3 on ebay) since Apple added compatibility for the new M2 Drives with High Sierra. They are much cheaper and have faster read/write speeds than the originals. OR there are some standard SSDs like this one you can buy if you don’t want to use an adapter: https://www.ifixit.com/Store/Mac/MacBook-Pro-13-Inch-and-15-Inch-Retina-Late-2013-Mid-2014-SSD/IF123-026-5

Just search for „MacBook Pro Late 2013 SSD“ on Google/eBay/Amazon and you will get some more results.