updating i747 s3 on TMobile

[dmc_lat47]

hi all:
some time ago, I purchased an unlocked at&t i747 from ebay, and have been using it with a T-mobile plan.

It is running the samsung version of android 4.0.4, and has never been updated in the couple of years or so since i've had it.

Is there any way to update the phone short of rooting and installing generic android on it? Maybe

I've tried checking for updates through the phone, but of course since i'm not on an at&t plan, no at&t servers are available to me.

I don't see anything on the samsung site.

thanks