How to downgrade from Lollipop to Jelly Bean on my Samsung Galaxy Grand? I upgraded my Samsung Galaxy Grand from Jelly Bean to Lollipop. it worked properly for one week, but then problems occurred. Only black screen is displaying on my phone . While dragging from top of the screen , it shows "No notifications" and it also shows time. Screen is still working properly, but i can't use my phone other than these. 
How can I downgrade my Samsung Galaxy Grand from Lollipop to Jelly Bean?
I would suggest to simply flash the desired version of Android for your phone. Surely, official images of Jelly Bean for Samsung Galaxy Grand exist.
Flashing a rom is really simple:
This instructions are for a Windows system, if you are using another OS just tell me.

Step 1: Install Fastboot on your Windows system

Download this file, it is an installer for the strict indispensable tools you need to put files on your softbricked phone from your PC.
http://forum.xda-developers.com/showthread.php?t=2588979
Install it and say yes both to the adb and the driver questions.

Step 2: Reload your phone to fastboot and flash CWM

When your device is turned off, connect it to your PC via USB and hold the power and volume down button. You should be in fastboot mode now.
Open a command prompt in Windows (Start --&gt; cmd.exe). Type cd C:\adb and then fastboot devices. You should see an hexadecimal code followed by &quot;device&quot;. If not, tell me in the comments.
Now download the file you find at this link, it is our recovery.
http://forum.xda-developers.com/showthread.php?t=2201860
Extract the .img file you find inside and rename it recovery.img. Place it in C:\adb.
In the command prompt, address this command
fastboot flash recovery recovery.img

Now reboot your phone to recovery using the power and volume up buttons. You should see the new recovery.

Step 3: Download the ROM and copy it in your phone

Download your desired ROM. Leave it as a .zip.
While your phone is in recovery mode, type adb devices and you should see again a code and &quot;device&quot;. Then move your rom .zip file in your C:\adb folder and address these commands:
adb shell
mount /data/
adb push nameofrom.zip /data/

Obviously replace nameofrom with the name of the zip archive of the rom you have downloaded. If you want, rename the zip to address the command with more ease.

Step 4: Install the ROM

When the push process has succesfully finished, navigate through your phone's recovery to install zip, install from internal memory or something like that. Select the zip you just pushed. It will start installing and, after finished, your phone should boot again upon reboot.