Under the terms of the Sale Of Goods Act, Argos are obliged to replace the original item, if not fit for purpose, but they are under no obligation to upgrade you. With that in mind, you need their co-op-eration, so you ned to be nice, rather than banging on the counter. Get hold of the manager, explain the situation, and reason with him that you will be delighted to advise everyone you know hnow good your local store is, and hopefully you can win him round. If not, there's little you can do - legally they are right to offer a replacement only.