As a benefit of being part of the ServiceNow Developer Program, those that have personal developer instances can optionally upgrade to the Helsinki release of the platform. We are providing this early access in order for registered developers to become familiar with the latest ServiceNow platform, leverage the latest features when building applications and to prepare for upgrades.
This optional upgrade is only offered on personal developer instances provided through the Developer Program. If you have a personal developer instance, you now have the option to upgrade on the My Instance page on the Developer Site. Under the Action menu, there is an option to "Upgrade to Helsinki". If you choose to upgrade to Helsinki, it is difficult to return to an earlier release for your personal developer instance.
All other instances (production and non-production for customers and partners) must be requested through HI’s instance self-service or through calling support. The upgrade to Helsinki will be available for all customers and partners in a few weeks.
More information can be found in the FAQ.