Downloaded images - Now what??

[sumlthomp]

I am totally new to this, so forgive me if my questions seem stupid. I have a couple designs that I would like to make into T-shirts. Once they are saved on my computer, what program should I use to open them & print? Word? Paint? Photoshop Elements? Also, are you supposed to adjust the size of the image when I open them? I have a couple designs that are intended for both adults and kids, is it best to measure their shirt widths to determine how to size the image? Any advice would be greatly appreciated. I have several to make, and want to make sure they come out just right. Thanks!