[ZipZapp]

I know this is a rehash post to some extent but as I look at older threads I am still unclear on my type of upgrade.

I have a 1st gen iphone.
I want to update it to 2.x.

My Operating System 1.1.3
My Modem Firmware: 04.02.13_G
My Bootloader: 4.6_M3S2
My Current phone is activated and jailbroke
On AT&T but not on iPhone service

Can I use Winpwn 2.5 to update this phone directly to 2.x.x and if so are there any pitfalls or settings I should use or avoid?

If 2.5 is a bad choice, what should I use to update the phone?

Thanks for your help!