Try
Gnu
Image
Manipulation
Program or GIMP for Windows.
It's free open source software.
GIMP - for Windows When you open a .png in Gimp you have the option in the toolbar at top of main window to scale the .png.
image>scale image.
After scaling image to size you want choose file>save as and and use the "select file type (by extension)" option (expand the +)
and select Microsoft Windows Icon to change from .png to .ico.
I use Gimp all the time, mainly for this purpose, works great.
I have thousands of icons I've picked up over time, many of them originally in .png form, lots of them recovered from linux distros (Linux uses .png's almost exclusively for icons).
GIMP does a great job of manipulating them.
I keep them in a folder in the root of my C:\ partition that I've named "Win 7 icons".
This way all my custom shortcut icons are in one place.