If you're using Blynk library, your code should be compatible with the new cloud. Some minor changes will be needed:
Update Blynk library to the latest version (v1.0+)
Add BLYNK_TEMPLATE_ID and BLYNK_DEVICE_NAME on top of your firmware, above any includes
Replace Blynk.notify, Blynk.email, Blynk.tweet, Blynk.sms with Blynk.logEvent. Read this guide on how to set up Events with notifications
Adjust indexing for Image Gallery, Menu, Icon, Segmented Switch, Icon Segmented Switch widgets. It used to start with 1, but in new Blynk it starts from the min value of the associated DataStream
Consider using Blynk.Edgent in your firmware for dynamic WiFi credentials provisioning
If you're using HTTP API, you need to update your server and request URLs.