Hello,
Sorry to hear you are having issues. Currently, Fences 6 not available on Steams. Soon perhaps. From what I know, there is no upgrade option for Steams version users. Perhaps, you can ask or request by raising support ticket using the link below, use the "Ask a Question" option. Include all information details. Remember to record down the ticket number for future reference if needed. Do not raise multiple ticket, that will make your ticket back to the end of the line. Send once and wait. Ticket will be answer by the order they send in.

https://stardock.atlassian.net/servicedesk/customer/portal/4/group/13 

Thanks
Basj,
Stardock Community Assistant