The motherboard swap is technically possible but not practical.

No, you can’t upgrade the 8GB of soldered RAM, and finding a motherboard with 16GB will cost you more than the laptop is worth.

The XPS 13 9350 has the RAM soldered onto the motherboard. There is no slot. You can’t send it to a service to desolder and resolder new chips — that’s a custom rework that doesn’t exist at any price you’d want to pay. Even if someone offered, the risk of damaging the board is high.

Replacing the motherboard with a 16GB version? Yes, you can physically swap it. But a used 9350 motherboard with 16GB runs $200–$300 on eBay. Your whole laptop is probably worth $300–$400. So you’d be spending 70% of the laptop’s value for a RAM upgrade, and you’d still have the same old CPU and battery. That’s not a good deal.

Better plan: sell this one as-is and buy a used XPS 13 with 16GB built-in. Or save toward a newer model that doesn’t cap you at 8GB.

This is one of those “it’s time to move on” situations.