1. RAM is not upgradeable
2. SSD is, in theory. But unlikely to be available to the public.
Best practice if you already have a Studio:
Get a fast TB3 enclosure with an m.2 MVMe SSD installed. You'll get about 1/2 the speed of the internal SSD, but for data storage & such, you'll likely never notice it. There is a lengthy discussion in this particular subform about it.
If you don't have one:
Carefully try to estimate your needs for the next 5-6 years. Choose your model conservatively. 512GB may be too little for an SSD, 2TB may be overkill. Getting a bigger SSD too cost-prohibitive? Consider the external option above. This is different for every user.