Let's see if Windows 10 Technical Preview can be updated to Customer Preview
Microsoft will unveil Windows 10 Customer Preview on January 21st 2015. It'll be interesting to see if Technical Previews versions can be dist-updated. This is something Microsoft has promised to do. However not all Technical Preview versions are going get dist-updates. In case you want try to update first install the latest official Technical Preview and wait for the Customer preview. If that doesn't work download Customer preview image and make a fresh install.