Great question! Very interested too since i’m approaching filling my SSD too 😅

Not sure if they have a guide, but the general idea is that you'd want to figure out a way to plug in that new drive, maybe via usb, so you can format it the same as the old drive and use a tool like rsync to copy over everything from the old drive to the new. Of course you'd have to shutdown all the running apps first before copying. When that's all done, you'll then physically replace the old drive with the new, and modify your /etc/fstab file to point to the new drive (depending on how the old drive was mounted).