You can only update your phone to Android 2.3.6 Gingerbread because there are no released versions of Ice Cream Sandwich for your phone. You can perform the update via air using Software Update from Settings > About device or using Samsung Kies.
If you want to update it manually, please download the version for your country from Samsung Updates, and run Odin which is found inside the archive you will be downloading. Start Odin, connect the phone, select One package option, select the archive which is in tar.md5 format and press Start. Wait for the flashing to finish and you have a working 2.3.6 version.