It is generally recommended not to "downgrade" from 1.25 to earlier versions (like 1.21), as this has been known to cause hardware errors, such as scanner failures where the machine gets stuck in a "Warming Up" loop.
To find the latest verified software and firmware for your specific model: Official HP Support Portal : Visit the Samsung SCX-4300 Laser Multifunction Printer series samsung scx-4300 firmware 1.25 download
Title: Samsung SCX-4300 Firmware 1.25 — Download & Install It is generally recommended not to "downgrade" from 1
: Samsung typically provides a firmware update tool. Run this tool and follow the on-screen instructions. The tool will usually detect the connected device and guide the user through the update process. The tool will usually detect the connected device
: Quickly press Menu → Copy → Left → Right → Menu → Right on the printer's physical panel.