Advanced folders are available only for Sync Pro.
There is no way to UPGRADE Standard folders to Advanced folders due to significant differences in their architecture. If you would like to share data using Advanced folder functionality, all you have to do is remove Standard folders from Sync and re-add them as Advanced folders (available in Sync Pro only).
STEPS TO TAKE:
1. Disconnect and remove Standard folder from Sync on all peers (Options > Disconnect)
2. Add the folder back to Sync: click on "+" -> Advanced and select the folder. It will appear in Sync on linked devices, or share the link with other peers not linked to your identity.