Since OP did not reply to us - I suspect he is at the process of re-installation, I did a quick search on the net.
(Since Duck is down I was reduced to use G 
gle)
https://www.google.com/search?q=zorin+16+upgrade&source=hp&ei=ZF-uYYToC4WVlwSohp24CQ&iflsig=ALs-wAMAAAAAYa5tdP_e0gOxkkbz4ttxb_qCex5HTUzu&ved=0ahUKEwiEqrq478_0AhWFyoUKHShDB5cQ4dUDCAc&uact=5&oq=zorin+16+upgrade&gs_lcp=Cgdnd3Mtd2l6EAMyBAgAEBMyCAgAEAgQHhATMggIABAIEB4QEzIICAAQCBAeEBM6FAgAEOoCELQCEIoDELcDENQDEOUCOhEIABDqAhC0AhCKAxC3AxDlAlCMB1iMB2ClCmgBcAB4AIABQYgBQZIBATGYAQCgAQKgAQGwAQI&sclient=gws-wiz
(good, Google got a wrong location for me)
I added the first result I saw in the Wall of Shame thread to caution members.