Edit: Google just announced the upgrade path to universal analytics:
We just launched the Google Analytics Upgrade Center, an easy, two-step process to upgrade your classic Analytics accounts to Universal Analytics.
From their upgrade instructions:
Step 1: Transfer your property from Classic to Universal Analytics.
We’ve developed a new tool to transfer your properties to Universal Analytics that we will be slowly enabling in the admin section of all accounts. In the coming weeks, look for it in your property settings.
Step 2: Re-tag with a version of the Universal Analytics tracking code.
Our goal is to enable Universal Analytics for all Google Analytics properties. Soon all Google Analytics updates and new features will be built on top of the Universal Analytics infrastructure. To make sure all properties upgrade, Classic Analytics properties that don’t initiate a transfer will be auto-transferred to Universal Analytics in the coming months.
Google will support upgrading and migrating data to the universal analytics, but that upgrade process is not ready yet. From their help document:
In the coming months, look for documentation to help you upgrade your existing Google Analytics web properties and data to UA.