Presumably you do not have rotation lock engaged?
If not, have you tried restarting or resetting your iPad?
Restart: Press On/Off button until the Slide to Power Off slider appears, select Slide to Power Off and, after the iPad shuts down, then press the On/Off button until the Apple logo appears.
Reset: Press the Home and On/Off buttons at the same time and hold them until the Apple logo appears (about 10 seconds). Ignore the "Slide to power off"
Just as a double check....
If you see a lock icon in the upper right corner of the screen - then the screen orientation is locked.
Try the side switch above the volume rocker first and see if that unlocks the screen. If that doesn't do it, double tap the home button and swipe to the right and look for the lock icon all the way to the left.
If the screen is unlocked but still will not rotate, reset the iPad.
Reset the iPad by holding down on the sleep and home buttons at the same time for about 10-15 seconds until the Apple Logo appears - ignore the red slider - let go of the button
Thank you but I know how to unlocked an ipad !
Reset, restoration nothing work.
Just find this link who expalins how to change the rotation in root but its not easy
I understand that you are having this problem, but the majority of us haven't had any issues at all with the update. That doesn't help your situation when you are going through something like this, but it really is the truth.
Anyway, I know that have tried restoring and that didn't help, but try this now since you have nothing to lose.
You can try resetting all settings. Settings>General>Reset>Reset All Settings. You will have to enter all of your device settings again.... All of the settings in the settings app will have to be re-entered.