2 things: your surface 3 has 64GB of storage, not RAM. While it may seem like a rather nit-picky distinction, it is rather significant. Basically, RAM affects performance if you don't have enough, storage is how many files you can store (your C drive)
Regardless, the RAM on all surface models is soldered to the motherboard and not upgradable. Surface Pro models have removable SSDs that can be replaced to add more storage but you have to remove the display first, a difficult process that usually requires replacing the display completely. Surface (non-pro) models have their storage chips soldered to the motherboard, preventing replacement.