If you are a CRM Online client and haven’t switched to Dynamics 365 from CRM 2016 you will get a notification sometime after June 1, 2017. What it tell you is that starting July 1, 2017 the auto-renew flag on your subscription will be turned off. And all customer renewals after that date will be forced to use the Dynamics 365 SKUs.
Transition to Dynamics 365 SKUs is not automatic however. You will need to work with your partner choose the correct licenses for your organization.