Please can smb tell how Can I upgrade my iphone 3GS ios 4.0.1 to IOS 5?

I have an Iphone 3GS IOS 4.0.1 and I'm really pissed off as I can't open most of the apps as they crash all the time.
Neither can i update apps as they require ios 4.3 or higher.
I would like to upgrade to ios 5 and then unlock the phone again.
My phone is not factory unlocked so i guess i'll have to upgrade and then jailbreak and unlock again… But the issue is that nobody i've asked knows how to upgrade to ios 5 now that ios 6 is out.
I don't want to upgrade to ios 6 as some friends of mine who did said their phone is either dead after the upgrade or crashing and doesn't support it well.
Please can somebody tell me how to do this?
Thank you very much in advance!
I would really appreciate some help.

Have you tried clicking on the upgrade button in iTunes when your iPhone is connected to your computer?

There's been a lot of new support for switching back to ios5 from ios6, so you should probably try searching for how to downgrade and following the guides. Same thing really.
Unfortunately you'll have to do a new jailbreak. Nothing around that.
I would highly de-recommend against ios6, as there's little support for jailbreaking it at the moment.
So try some of the new guides out there.
Here's one courtesy of google: http://www.maclife.com/article/howtos/how_downgrade_back_ios_5
Best of luck.

Connect your phone to itunes and check if an update is available. If it suggests ios 6, than ull have to manualy download ios 5 (google for it) and manualy update by clicking shift+restore.