Sony Ericsson did not officially release Android 2.3 for the W8 hence there is no official way of gettting it. However you can get it thanks to the developers of XDA there are many custom Android 2.3 ROMs available at XDA you just have to play around with them and try them out to see which one is best. I personally recommend GingerDX.
1) To install a custom ROM you first have to root your phone.
2) Now you install Clockwork Recovery Mod.
3) Wipe data and install custom ROM via Clockwork Mod.
4) Reboot and enjoy!
Different ROMs may have different procedures and requirements (e.g. different kernals) I recommend that you stay on the stock kernal as installing custom kernals can void your warranty and possibly damage your phone.
To root your phone and install clockwork mod use X8 Toolbox found here.
For custom ROMs check here.
BTW most things built for the X8 will work on the W8- both phones are the same, just have different branding.
