My paperboy and good friend dana was looking for some advice yesterday on making a digital file larger in printable size.
I thought i would share some of that advice.
If you want to make your image bigger in height and width:
1) go to image - image size
2) make sure constrain proportions is checked
3) if your files resolution is higher than 200dpi then uncheck the resample image box and change the resolution to 200dpi.
4) hopefully that will get you close to your target size but if not, check the resample image box, set the dropdown menu to bicubic smoother (it should be on bicubic by default), and start scalling upwards in size in 10% increments.
5) after you hit ok to the first 10% adjustment you will have to go back to image - image size and type in the next 10% jump and also set the dropdown menu to bicubic smoother again (you can set a new default by going in to photoshop preferences under the general tab and change it if you like).
If you want to make your image smaller with the image size dialogue box:
1) go to image - image size and check all boxes.
2) set the dropdown menu to bicubic sharper and type in the dimensions that you want.
Personally i just use the crop tool and set the size i want in the options bar when i am shrinking something.