~AlphaFlame~
I'm assuming you have Windows, therefore I'm assuming you have Paint. Open the .png however you can, copy it, move it to paint, and then click the select rectangle option (I believe that's what it's called)... then, select the area you want to show. In the bottom right, you'll see two sets of numbers like "32,39 | 29,49"
The two on the left are the x/y, and the second two are the width/height...
Tada
