A brief guide on how to to upgrade samsung galaxy fit to Android 2.3.
1: Goto samfirmware.com Galaxy Fit page:
Login - www.SamFirmware.com
2: Download the 2.2 FROYO firmware labelled S5670XXKB1 (This is a russian firmware but you can easily change language to English)
3: Flash the firmware over your current one with help of ODIN. Follow the guides at samfirmware.com
4: Install the latest version of Samsung Kies 220.127.116.1144-11
Link: Download Samsung Kies 18.104.22.16844_11 Free - Search, browse, download and manage apps for mobile devices - Softpedia
(Install on a OS other than windows 7, as firmware update does NOT work on win7. Xp worked for me.) You may also have to isntall .net framework 4 & windows media format 11. Search for the links on google.
5: Connect your Galaxy Fit with S5670XXKB1 & Kies will popup message a new firmware is available.
Firmware details : S5670XXKPF (GINGERBREAD.XXKPF)
6: Follow the steps to update firmware through Kies.
7: Change the language back to English from Russian.