Forum Moderators: not2easy
To resize your entire document (in your case, the single image) go to:
1. Image > image size
2. you will be given 2 sections: Pixel Dimensions, and Document Size
from here, it depends on what your intended usage of the image is.
you most likely will want to change the top options (pixel dimensions), which will change your on-screen size, relative to 72 dpi. (your screen's resolution).
If doing this, ensure that "Resample Image" and "Constrain Proportions" is selected.
If you need to upscale a digital image yet retain it's quality
> open the image (use camera raw or non lossy format - e.g. TIF)
> open the image size dialogue box.
> set the image interpolation method to bicubic smoother
> and then resize it in 110% increments.
You can turn a postacard image to a poster, really you can! For some reason unbeknown to me the image will keep its sharpness much better this way than if you just blew it up to 200% from the original.
I have made an action with this and use F11 as a short cut to do it quickly. Great tool for photo resampling.