Family 6 Model 7
indicates that you have a Slot 1 Katmai
based Pentium III.
The fastest avaliable Slot 1 processor would be the Copermine Pentium III 1000MHz
, but this may or may not work in your specific system (chipset and BIOS dependent).
At this point, your system is only really useful for running depreciated OS' and playing legacy games.
It would make no sense at all upgrading as even the most inexpensive machine available today is massively more powerful.