we are supporting the last 4 major production ready releases. We have just released 4.13.0, which is currently not marked as production ready. So we are currently supporting 4.9. to 4.12.
For your second question, you cannot directly update from 4.8. to 4.12. there were a lot of technology changes in-between. If you want, we are happy to support you with this update and guide you through this.
All KNIME Server subscriptions come with a support subscription, you can open a ticket with our enterprise support team by sending an email to support@knime.com and they will come back to you shortly.