Needs a little advise on upgrading firmware

[fiberwalker]

If I have a recently hacked blackrain iPhone 2 which has firmnare 3.12 installed. Can I upgrade the 3.12 to higher such as 4.3 or above as many apps. cannot be played or installed on this lower version 3.12 as its requirement is usually above ver 4. So will it cause any conflicts on this set should I do a upgrade? Thanks in advance.