Sometimes art assets need to be tweaked before they are added to a game. Resizing is one of such tweaks.
So, how to change beautiful into small?
The answer is ImageMagick

After install the magic of resizing is done like this:

convert fileName_* -resize 32x32 newFileName_%02d.png

Parameters are described in official documenation https://www.imagemagick.org/script/convert.php, and in numerous tutorials, such as https://www.lifewire.com/convert-linux-command-unix-command-4097060

But the joy of resizing is not enough for us, is it? It would be nice to create a sprite sheet from nice and small tiles. This can be done with:

montage -background transparent -geometry 32x32 newFileName_??.png spritesheet.png

In my case 83 png tiles were 256 by 256 pixels with total size 21 Mb. After conversion to tiles 32x32 the total size is 73 Kb.