M258 controller - How do I upload program with USB

[noparking]

Hi 

I have a an Modicon M258 PLC and need to interrogate the program in order to find what is wrong with the plant! How do I upload? I understand this can be done with a memory stick. If so , will any new clean/empty stick be acceptable and is  size critical. I also have the SOMachine s/w but do not know the IP address. 

I am quite nervous regarding this task as no-one has a copy of the program and the controller is used 24/7. I've phoned Schneider but "all engineers busy"

Can any one out there  help