That’s the tests-passed version, that’s recommended for most folks. It gets all of the updates and latest features.
Since the disk size is smaller on the new 1GB droplet, you can’t just resize it. What you need to do is create a new droplet, install Discourse , download a backup from the old server, update your dns, restore the backup to the new one.
The other way to go is to resize to the new 2GB droplet and run discourse-setup to change the memory settings to take advantage of the additional RAM.