you can activate change the tickrate in your game server by two way
1) Using the command line parameters in your game panel
a) build a new command line
b) add the command -tickrate 128
c) preview the command line comparing it with the default command line
d) Save
2) Adding command in your configuration file
a) rate "128000" cl_cmdrate "128" cl_updaterate "128" cl_interp_ratio "2" cl_interp "0"
N.B If this commands create problem to the server you can simply go back removing it.
More command are available to improve your setting performance please "google" to find best setting for your server
