Q: I bought an iPad mini4 specifically to use with a Phanton3 pro drone. It will NOT link the remote with the drone. They say it is an iPad mini 4 9.3.3 software problem. How do I delete and reload this.

Apple frowns on downgrades.

While Apple allows, try downgrading to 9.3.2.

For a limited time Apple will allow you to downgrade to the previous release.  Hurry do not wait.  This period lasts for at most a week.

See brownox second post here:
https://discussions.apple.com/thread/6545455
and
http://www.gottabemobile.com/2014/09/17/downgrade-ios-8-to-ios-7/

see what versions are allowed:
http://api.ineal.me/tss/status

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see the post by arizonacat and others in this thread.

https://discussions.apple.com/thread/5337442?tstart=0

arizonacat points out these sites:

• Provides easy access to Apple firmware files.
  http://www.ipswdownloader.com/
  
  
• How to install the ios software.  The install will erase your exiting data. Backup your existing data.
  http://osxdaily.com/2010/11/23/how-to-use-ipsw-files/
  

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See second procedure about reloading software from scratch.

Re-boot ipad.

Press and hold the Sleep/Wake button until a red slider appears, then drag the slider. Then press and hold the Sleep/Wake button until the Apple logo appears. 

https://support.apple.com/en-us/HT201559

force power down if the above give you trouble.

Hold down both the Sleep/Wake button and the Home button. Ten seconds or more.  Hold until the Apple logo appears.

more details on re-booting:

    http://ipad.about.com/od/iPad_Guide/ss/How-To-Reboot-Your-iPad-Power-Off.htm

This these tips by MichelPM to improve performance:

https://discussions.apple.com/message/29504169#29504169

https://discussions.apple.com/message/29504311#29504311

Restore to factory settings by loading the latest version of ios that your machine will support:

   1)  Do a full backup of your device if needed.  Twice is best -- cloud and computer.

       https://support.apple.com/en-us/HT203977

   2) Three ways of restoring your ipad.  [ as easy as abc ]

   2.a) "You can use iTunes to restore your iPhone, iPad, or iPod touch to factory settings and the latest version of iOS."

          http://support.apple.com/kb/HT1414?viewlocale=en_US&locale=en_US

   2.b) Be a little more insistent:  "You can put your iOS device into recovery mode, then restore it using iTunes.:

          http://support.apple.com/en-us/HT201263

   3.c) At last resort you could consider DFU (Device Firmware Update).  This could void your warranty.

          http://www.imore.com/tip-put-iphone-ipad-dfu-mode

Since iOS 9.3.3 is new not all apps support it now so keep checking the apps update an when you update it try it again.