sgunhouse, sorry, I can't understand which folders do you mean. But thank you for answer anyway!
In my case I'm interested in deleting openned tabs information from Opera Sync server for the specific old device. Do you suggest booting this old device up, then closing all openned tabs in Opera Mini and then deactivating sync in device's settings?
I ask because I tried to close some tabs on this device but they didn't disappear from Opera Sync page (I tried to reload this page on pc several minutes after, closed tabs were still shown).