Hello JamesA,
There is no real concept of a main scanning server. Every scanning service is treated in the same way. However, some customers mark the servers that also holds the database and/or website as the main scanning server.
The article below describes indeed how to move as scanserver, which is not the same as you are doing. But the script mentioned in the end of the article normally moves the scanning targets to a new scanning server and deletes the one you don't need. This might be a different scenario than yours.
Move your installation to a different server - Lansweeper
If you want to remove a scanning server, you can simply click on the red icon on the scanserver tab under the Scanning menu. But before doing that, make sure to create your scanning targets also on the new scanning server. This will be a manual action though.