RobotStudio event

How to control payload

Hello all,
  I am working in IRB1600 specs are 1.45m reach and 6kg payload. IRB1600 1.45m reach robot having 8kg payload too.
Both model have same hardware setup?? Is it possible to control payload limit in software?? In IRB1600 is it possible to increase payload from 6kg to 8kg ??
Actually i am doing machine tending project with IRB1600 . My old project payload is 5.1kg. Now client changed some other variants , current payload is nearly 7.3kg. 
If there is any other solution to solve this problem pls let me know. 
If it possible pls,add the procedures to increase payload.

Thx in advance