Greetings,

can any one tell from where can i download Gefanuc trail software to make a small modification in 90-30 Gefanuc PLC

If you are a registered GE fanuc customer you might want to try at the global GE fanuc tools&support section > controllers & I/O > Software downloads > Developer downloads.
But I doubt you will find a demo version there cause mostly this is available for everybody.

At the GE Fanuc website you can download a version of Logicmaster 90 software for the 90-30, but that will only help you if your program was originally written with Logicmaster. If it was written with VersaPro or Proficy (Cimplicity) Machine Edition, Logicmaster won't be able to modify it.

The version of Proficy Machine Edition for the 90-30 is not particularly expensive as such things go. Contact your local GE Fanuc distributor.