If you've already purchased the Microcontroller Beginner or the Intermediate Kit, you can purchase the upgrade kits for the Beginning to Intermediate or Intermediate to Advanced.
The Beginner to Intermediate Kit features everything included in the Intermediate Kit minus everything you've already purchased in the Beginner Kit.
The Intermediate to Advanced Kit upgrades you to the Advanced Kit components like the Accelerometer and Ultrasonic Range Finder.
Bonus: Upgrade to the Advanced Kit from the Beginner Kit and receive $5 off the original price.