How and where to set the "gw/acl_mode" to 0 (zero) ?

Hi Experts,

I am getting Error - 748 during RFC connection test in SAP ECC to SAP PO 7.4 JAVA only. I have got the details as it is because of Gateway security parameters in SAP PO, like to know where we need to maintain the parameter "gw/acl_mode" to 0 ? is that we need to log in to server to do these changes ?  step by step guide will help.

Thanks,

Tamil