If you use a MacBook or a Magic Trackpad, you can use a gesture similar to the Windows mouse method:
For a specific pixel size (not just small/medium/large): change desktop icon size
He remembered a trick his tech-savvy cousin once mentioned. He clicked on a blank spot on his wallpaper, right-clicked, and hovered over A side menu slid out like a secret drawer. He saw the options: Large, Medium, and Small. He clicked 'Large.' If you use a MacBook or a Magic