You can try to sell them, but I suspect only a hardcore collector would want any of these. The info. in them is all outdated.
If you don't want to sell them, you can try to donate them somewhere - but I'm not sure who would want them. I had a subscription to the SWI myself years ago, and found myself with a large box of these back issues as well (I had let my subscription lapse - since, like I said, the info. in them was all outdated even right after it was released). They were taking up valuable room, so I ended up donating all of them to my local library. A couple of months later, I was putting some cardboard boxes in the library's recycling bin (which was in the parking lot), and noticed all of the SWI mags. I had donated, thrown in the bin - LOL. I guess they had less use for these than I thought. In any case, at least they will be useful somewhere - i.e. ending up as recyclables is better than being thrown in the trash & ending up in some landfill.