Outdated information, just set the registry entry HKCU:\Control Panel\Cursors\CursorBaseSize to anything above 32 and call SystemParametersInfo in user32.dll to refresh (or restart). I've written a power shell script that lets me
change cursor scheme and size with 2 clicks...

Would love if tools like this would be more flexible at cursor size too...
1. Don't assume cursor having aspect ratio 1:1
2. Don't limit size to 256, 512 or anything rather the technical limit (2^8 for .cur, 2^32 for .ani)

Although the default options only allow you to change the size to 32 and 48 pixels, the most commonly used sizes these days, you can actually change to another format by just typing the number in the first field. If you dont want a square, type both numbers like "24x40". I would not use sizes above 255, because there is just 1 byte in the .cur and .ani files that specifies dimension, so the file would be invalid.

SOLUTION: TO CHANGE THE CURSOR SIZE, CREATE A NEW FILE AND ON THE RIGHT OF THE SCREEN THERE IS AN OPTION: "CANVAS SIZE". DOUBLE CLICK ON THE DROPDOWN MENU AND TYPE IN THE SIZE YOU WANT LIKE THIS: 64x64 FOR A CANVAS WITH 64 BY 64 PIXELS!