diyguide

Hi all, I have also found this thread helpful. My query is what is the best way of trying to increase the quality/resolution of images? For example, I have some 1024 dds's, as well as bitmaps and png images that I would like to try and resize to 2048. I also have 2048 ones I'd like to get to 4096. Just experimenting, understanding that it is likely easier going from higher to lower sizing in terms of quality. I have PS, Gimp and Paint etc and high end pc. Thanks in advance.