Nexus S 4G GRJ90 Update Download
Here is the link for the Nexus S 4G update (GRJ90)
This link is directly from Google's server (once you know the file name, it is easy to locate)
Here are the steps to update
Note : You must be on GRJ22 to use this update method
Step 1 rename the file to update.zip.
Step 2 Copy update.zip to root of SDCARD.
Step 3 Power off phone.
Step 4 Press and hold Power+Vol up buttons(Enters Boot loader).
Step 5 Select Recovery.
Step 6 Wait for the Exclamation Indicater, or Press Vol up and Power, if thats does not work , Press the Power button, or Vol up.
Step 7 Recovery menu options should appear, select apply update from SDCARD.
Step 8 Enjoy