down load os sierra

It depends on the year on these. 2009/10 model go up to 10.11, but the 2011 can run up to 10.13. However, the issue with the 2011's is the GPU failure means you either hope it lasts a while or you need to permanently disable the GPU using the dosdude1 tool because ALL of them will sadly fail in due time.
Note: The GPU can be soft disabled, but this is easily undone with an NVRAM reset. It's better to permanently disable it. You also lose the 2nd monitor option as well when you disable it, and that goes with the soft and hard disable methods.

I looked into this because when I got my 2011 MBP after an issue with an A1181, yes I did look into getting another 17" since I had the 2009 AG. What ended the search was the GPU problems. If it wasn't for these bad GPUs I'd have a 2011 17", and I'd happily deal with the weight for the true AG panel, even seek it out.
It's truly sad -- the 17" was coveted for the screen (even in the rMBP era) for years even after they were discontinued.
Then the GPU problems that came up put the last truly desirable 17" into the history bin to be lost to time as there is no permanent fix without compromising the option to run dual displays. To this day, I still love the old 17" Unibody myself (and really wish when the M1/M2 16" came out they put out a notch-less 17.5" version as an option, even if the webcam was marginally worse) but the reality is it's so freaking close losing 1.5" of screen space is just a nitpick; the Mini-LED DCI-P3 screen blows that concern out of the water to a non-concern. The color accuracy P3 offers instantly made up for that exclusion, in addition to bringing back the ports. It has the weight of the 17" at 5lb for the M2 versions but really is anyone who wants one going to look at the weight and freak out? We're fine with that to have our 17" MacBook Pro again with modern processors that's the tradeoff and Apple knows it. It isn't being sold to travelers.