Update jailbroken iPhone

I have a jailbroken iPhone 3gs with os version 3.1.2 I was wondeing if it's possible to update it to a more current os if it's possible please let me know how or supply a link. Thanks

 

yes you can update to 4.1 firmware using Sn0wBreeze 2.0.2.

But first you need to know which bootloader you have, new or old? (google how to find out as it's too long to explain)

 

I tried to install that source to cydia but it says it's invalid. can you post a link to a guide

 

Sn0wBreeze must be downloaded through your pc/ laptop / mac whatever you have.

But.....for 3g, you have to have either:

new bootrom with 3.1.2 or 3.1.2 shsh saved or

old bootrom, and jailbroken with spirit or jailbreakme.com

use idetector from www.ih8sn0w.com to find out the bootrom