Android 2.3.1 is ready to download from Google servers, if you don't want to wait until you get it OTA.
- Download the file from Google
- Rename it to update.zip, and place it on the root-directory of your internal storage
- Reboot your phone by restarting it with holding volume up and powering back on
- With the volume buttons you need to choose "recovery" from the list, and select it by pressing the power button short
- When you see the triangle on your display, press volume up and power once again and you'll see a list of options. Select update. This could take a little while then. Let it go through.
Source: Android Central
