first of all, the modem is provided to you by PTCL and you don't own it. therefore any damage done to it might get you in trouble. If you get ur modem bricked (software damage), then PTCL may have some procedure to follow.
If you own a modem and want to upgrade, first looking for the CHANGE LOG of the new firmware, if you find any bugs being fixed then you must go with it. Performance really depends on various factors, if your modem got some kind of bug or software issue which new firmware may resolve, will help you improve your performance.
Final thoughts, I would not encourage you to update the firmware unless you are having any technical issue with modem, like modem restarts, Wifi signal issues (if its a wifi), Internet disconnection etc...
Note: Always do firmware upgrade with a power backup, the power loss during upgrade might damage the device.