When you need to submit an app, I recommend you to have a look at this:

[LI CHENG Vanessa]

I recommend a web to resize your app icon automatically, since you'll need prepare many sizes when submit an app to iTunes or Google Play.

makeappicon.com (Why not saving it, coz you may need it later.

[Deanna Earley]

Post by LI CHENG Vanessa
I recommend a web to resize your app icon automatically, since you'll need prepare many sizes when submit an app to iTunes or Google Play.

You realise that win32 apps (as you're in a Win32 UI group) have no way
to target iOS or Android?
Furthermore, multiple sized icons have been the norm for 20+ years in
the Win32 system and as such we already have tools for it built into
most of our IDEs.