If you're using windows, just follow Nintendo's advice, but if you're using macOS / OSX you end up with annoying error messages telling you your card is corrupt. It took me ages to figure this out, so I thought I'd share. I read this post and was convinced it might not be possible, but I just upgraded my 128GB card to a 256GB without losing (or having to re-download) any content. Hope this helps someone here.
Steps are as follows:
- Backup the Nintendo folder from your original SD card. You can just drag and drop it to your Desktop, but just to be on the safe side I ran Disk Utility and selected File -> New Image -> Image from "disk2s1". Your SD card may be named differently.
- Format the new SD card in the Switch
- Eject the old SD card and insert the new SD card into your mac
- Copy contents of the Nintendo folder from your copy onto the new SD card (if you did it via an image, then double-click on your image file to mount it, then copy from there). Select Replace all files if prompted.
- Wait for ag