If you want to use your existing self hosted instance in the cloud, it will essentially replace the demo instance you have setup. (You can’t merge your existing board with another board, regardless of its CIC or self hosted.)
Just reach out to the sales team and they can get you setup with the conversion team.
In a nutshell, you would agree on a date in which to take your community offline. You’ll do an export of the database and all of the site files. You’ll zip those up and upload them to a location provided by IPS.
The staff will import your database and IPB related files (attachments, plugins, etc) into the CIC platform.
Once ready, you’ll need to fix any custom themes and update any third party resources you might be using. Finally, you’ll then switch your DNS to them and your new site will be live.
Make sure you have a full backup on your end before you start. They’ll highly recommend you do this so be prepared to do so. 🙂