You first need to uninstall Forcefield from your child's old phone. To do this from an iPhone, iPad or iPod, go to Settings > General > Device Management. Select Forcefield MDM and tap Remove Management. Enter the device passcode if required. Select Remove. To install Forcefield on your child's new iOS device, download Forcefield for Child Device from the App Store and follow the prompts.
Do do this from your child's Android device, select Forcefield for Child Device and drag to trash. If prompted, tap Manage Device Administrators and uncheck Forcefield for Child Device. Tap Deactivate. Under "Apps with usage access," tap Forcefield for Child Device and toggle "off." You will then need to re-drag Forcefield into the trash. Other Android devices may require you to go to Settings > General > Security > Device administrators > Uncheck Forcefield and tap on Deactivate. Go back to Security, scroll down to "App with access to usage data" and uncheck Forcefield. On the device's home screen, re-drag into trash. To reinstall on an Android device, download Forcefield for Child Device from Google Play and follow the Installing on Child Mobile Device FAQ.