[otrs] To change logo in agent interface

Hi, I'm using otrs 3.0 and would like to know whether we can change "OTRS" logo @ right side corner of agent interface.i couldn't get otrs image in images folder. Also i tried changing productname in config and it only changed logos at browser header,login etc but not OTRS logo @ rightside corner of every page. If somebody have tried this,please let me know Regards Ravi Shankar