From the .1 increase in the version number in Android 4.1 Jelly Bean, it's quite evident that the new version of the OS is not a revolutionary update like the Ice Cream Sandwich. However, Jelly Bean does include some exciting new features and major tweaks, including a Siri-like voice assistant, an improved Home screen, Project Butter, Google Now, improved camera app, smoother user interface and better keyboard, among others.
If you are a Nexus S user, desperate to experience Jelly Bean, you have two options to get the update installed on your device - either wait for Google to send it to your device as an OTA update or install it manually.
Below are the steps to follow for a manual installation of the Android 4.1.1 Jelly Bean on Nexus S. But before going ahead, please note that IBTimes will not be held responsible if any user loses data or the device gets damaged while following the steps explained below. Users must proceed at their own risk.
Step 1: First of all, unlock bootloader, root and flash ClockworkMod Recovery on your Nexus S. For more information, click here.
Step 2: Now, download Android 4.1.1 Jelly Bean (JRO03E) [Direct Download - Google].
This .zip file is for update to Jelly Bean from Android 4.0.4 (Build: IMM76D) on Nexus S models i9020T / i9023. According to some users, this .zip file also works on the i9020A model, even though it is not supposed to.
Place the file directly under /sdcard on your Nexus S's internal storage.
DO NOT use this .zip file if you are not on Android 4.0.4 with the specific build number previously mentioned.
Step 3: Now, you need to reboot into ClockworkMod (CWM) Recovery by shutting down your Nexus S, and then pressing and holding Volume Up + Power buttons.
Step 4: Take a NANDroid backup. This will be helpful later on in case you find any issues with the Jelly Bean ROM.
Step 5: Navigate to install zip from sdcard > choose zip from sdcard > [the .zip file that was downloaded in Step 2]. This will flash Android 4.1.1 Jelly Bean to your Nexus S.
Step 6: Now, select reboot system now from CWM's main menu.
[Source: Redmond Pie]
Your Nexus S should now boot into Android 4.1.1 Jelly Bean.
For any queries, check out the official thread over on XDA Developers.