I need MS paint help

[Nitram]

How do I shrink an image to pixel size and keep its H/L ratio?

I did it once for my current rockin' avatar but I want a new one for multi-forum use and I can't figure out how I did it.

 

[Nitram]

What I mean is, how do I get a non square image to keep its hight length normality without having to do all that math, I know MSpaint has a way to do it >_<

 

[Oropher]

image >> strech/skew

change height and width by same percentage.