Hello, Phornpimol Klompanya.
Welcome to Microsoft Community!
I understand that you currently have the need to upgrade your SSD, the Surface Pro 7+ can support up to 1TB sized SSDs, and that also includes the 512GB and 256GB sizes. I have found the relevant images of the SSD for you, this is a removable SSD:
I also found the following guide link for you if you wish to do your own SSD replacement or upgrade on your device. Please make sure you have the proper materials and tools to perform the disassembly of your device.
SSD replacement is included in the demo video:
Microsoft Surface Pro 7+ Repair - iFixit Repair Guide
Disclaimer: Microsoft provides no assurances and/or warranties, implied or otherwise, and is not responsible for the information you receive from the third-party linked sites, or any support related to technology.
I hope you stay safe.
Best Regards.
Leo.L - Microsoft Community Support Specialist