I need to change gateway settting for LAN and cannot find it in the configuration menu.
The only setting/change I find is the WAN configuration.
Can anyone help?
Are you talking changing the address or some other configuration? Gateway address is under the Network menu.
The VBP can only have one gateway address which is associated to the WAN IP address in the web GUI. For the LAN side, you have to add a route using the LAN gateway. Without any routes, the VBP will reach any device ont he same subnet as the LAN side IP address. Adding routes (System > Routes) will give the VBP the ability to reach your other LAN subnets.
I have included a screenshot of my VBP which shows some of my subnets.