His grandfather, seeing the phone back in action, nodded approvingly. “You fixed it yourself. That’s better than buying a new one.”

Since Nokia's official update servers (Nokia Suite/Ovi Suite) are no longer active for legacy S40 devices, you generally have to use third-party tools to flash the firmware:

: Often used to find and download the specific 8.75 firmware files (flash files) before installing them via Phoenix. How to Install Firmware 8.75 Download Firmware

Disable launchpad animations, delete old SMS threads, and move apps to mass storage. This often improves speed more than a firmware update.

Here is the realistic situation: