set proportional editing tool size using keyboard

While using the proportional editing tool (“o” key shortcut) I can control the tool size using the mouse scroll button.
Is there any keyboard shortcut to control it ?

After move - rotate - scale - - - - - -> F6

pg up/down

I’m on a laptop, and Blender doesn’t recognize my PgUp/PgDn keys, but the touchpad is set to scroll on the right edge and that does the same as the mouse scroll wheel.

Thanks for the help guys! page up/down worked.

Am on my desktop and F6 didn’t worked.