First download the recovery tool from here - Recovery Tool
Then, follow the steps below:
•Insert your SD card into the SD reader port on your PC or via a USB SD card reader - this should appear as a removable disk under your computer menu
•Double click the Vtech Icon located in your downloads folder to run the program - Click Continue
•Click 'Make Recover Program Card' then click 'Next'
•From the drop down menu, select the removable disk drive allocated to the SD card (drive E shown for demonstration purposes, the actual drive allocated to your SD card may differ)
•The application will now format the SD card with the Storio factory default operating system
•When the following screen appears, remove the SD card and then re insert it into the SD port or reader to complete the format
•Once the format is complete the following confirmation will appear - please click OK and follow steps 1-5 to finish restoring your Storio to factory standard.
•Please note, once the process is complete, you will need to re run the program to 'revert' the SD card back to a usable state