How to unlock buttons of dell IN2020MB monitor

Hi everyone,

I have IN2020MB monitor but i am facing a problem with my monitor and i don't know where is my user manual that's why i cant find how to change setting of my monitor, i cant find the button to decrease the brightness of monitor because it is showing lock symbol on the screen and i don't know how to unlock it and another reason is this i don't like brightness. Its harmful for my eyes even everyone's eyes we should not work on computer in the high brightness setting.So i wanna know how to decrease the brightness of my monitor can anyone tell me...?
Thank you and i am waiting for answer!

You need to press and hold button just above power button for about 15-20 seconds and should be unlocked. Now you can use OSD and do things you want.