Can I change the resolution of a png from 120x120 to 180x180? I have a 120x120 png and I need it to be converted to a 180x180, is this possible using iPhoto or other Apple software for a mac? I do not care if the picture turns out good or not I just need it to be that size. I am running OSX Yosemite.
Open the file in Preview

Now Click on Edit

In Edit menu bar click on the last icon looks like a square with line from corner to corner.

In the new window you can adjust the size and the resolution.