The 2017 MacBook Pro models came with or without the Touch Bar. The models that came with the Touch Bar had soldered in storage devices to the logic board and therefore cannot be upgraded. The model that came without the Touch Bar has a proprietary storage module which can be replaced. Which model do you have?
There is more information in ➔ This Community Discussion.
If you have the model without the Touch Bar then ➔ This YouTube Video shows what is involved to replace/upgrade the storage module.
I recommend that you do a thorough research, depending on the model that you have, and make a decision.
Axel F.