Downloading Nexus One Update
First step in the process of updating your Nexus One to Android 2.3.3 is to download. This can be done through links available online for free, and is done in an easy manner. Try the same action again if you are unable to get it downloaded for the first time.
Renaming File to Zip File
Once you download the update file, rename it to an Update.zip file. If your operating system somehow hides the file extensions by default, just rename the file to Update, as if you do it Update.zip, the zip extension is repeated twice as Update.zip.zip, which will not allow you access the file. It will not open.
Connect Nexus to PC
Next step is to connect your Nexus One mobile phone handset to your PC or laptop. Once connected you transfer the file to root of the microSD card. It is not a difficult task to perform, and apparently you should not face any difficulty.
Once you transfer the file to your computer, press down Power button to reboot your Nexus One. Rebooting process is done or achieved by pressing Power and Volume Down buttons on your Nexus One. Both buttons have to be pressed down at the same time, pressing any one of them will not help.
Once you reboot your Nexus One, you will see a screen with Androids on it. What next you have to do is to use the Volume keys to navigate to Recovery and then press Power button. Your recovery screen display a triangle button with an exclamation point on it. Just press Power and Volume Up button to get your recovery screen once again. You need to press both buttons at the same time.
Application of Update.zip file
You are only a step away from update your Nexus One to Android 2.3.3. Just use the trackball, and scroll it down to select the 'Apply sdcard:update.zip.' file to start the updating process. It takes only a short span and your phone is updated. You can start using and enjoying your Nexus One manually updated to Android 2.3.3.