Say I've got a question about how to do something, if I find the exact same question but specified to a software that I don't have access to, should I edit the original question so that the question is broader or do I duplicate the question this time specifying the software I want to use?
I would say that you should post a new question.
If you edit an old question, which has an accepted answer, there would be less incentive for people to answer it. A fresh question gives you the power to mark a question as accepted, and lets other people gain reputation.
Besides of Devdatta's point that you probably won't get many new answers to an old, accepted question, there's also the issue that someone had a very specific request (for good reasons or not) and I don't think it would be appropriate to just go there and remove the specifics.
As a general rule of thumb I'd recommend posting a new question - maybe linking the old one.