Disclaimer: The procedure given in this tutorial is considered as risky and may cause damage to your phone. It is recommended that you should not follow it unless you are familiar with these things. Follow this guide completely at your own risk.
I. Before You Begin:
1. The following procedure works for Samsung Galaxy Ace GT-S5830 smartphones.
2. Make sure your device have at least 80% battery power.
3. You must have ClockworkMod Recovery installed on your device.
4. Make sure USB Debugging is enabled
II. Downloading Required Files:
1. Jelly Bean 4.2.1 ROM For Samsung Galaxy Ace S583 [Filename: cm-10.1-20121231-UNOFFICIAL-cooper.zip]
2. Google Apps [Filename: gapps-jb-20121017-KonstaKANG.zip]
III. Install Android 4.1.2 Jelly Bean ROM on Samsung Galaxy Ace S5830:
1. Connect your phone to PC using USB cable.
2. Copy downloaded files to the SD card of your phone.
3. Disconnect USB
4. Turn off your phone
5. Boot into recovery by pressing and holding Volume Down, Home and Power buttons
6. Wipe the Data and Dalvic Cache or you might brick your device afterwards
7. Select install zip from sdcard, then select choose zip from sdcard. (Locate the Jelly Bean 4.2 Rom .zip file) and select it by pressing Power button.
8. Once the ROM installation process end, repeat the step 7 but choose Google apps instead of ROM zip to install the Google apps package.
9. When installation is completed, go back to the main recovery menu and select reboot system now to reboot the phone and boot up into customized Android 4.2.1 ROM
Congrats! Well known and super customize Android 4.2.1 Jelly Bean firmware based custom ROM now installed and running on your Samsung Galaxy Ace S5830.