Help needed: 3gs on 3.1.3 to 4.x or 5.x unlockble

[purpl7duece]

I have my old 3gs I want to give my mom to upgrade from her 3G. I am more of a hardware geek than a software one, but have some knowledge on that side. What is need to upgrade to 4.x or 5.x and still stay unlocked? It's currently on 3.1.3 with 05.12.01. I will be using a PC with Windows 7 to perform the upgrade. Thank in advance!

[iYeow]

Is your iphone currently jailbroken ? Do you have any saved shsh blob ?

[purpl7duece]

The phone is jailbroken and unlocked. It does have them saved

[iYeow]

Then you can restore to any firmware with saved blob by restoring to custom firmware.