Change default route with two interfaces

Hi experts,

I'm running 6.7.2 with two network interfaces, one to my office network, the other one to the dmz.

By now the default route is set to the dmz, but then I don't have access to the internet (for firmware updates etc.) as the dmz ip is not exposed to the internet.

I want to change the route to use the office network, then I have access to the internet via NAT.

My route settings are (on the GUI):

IPv4 default 10.0.1.1 via br1 metric 1

IPv4 10.0.0.0/24 br0 metric 1

IPv4 10.0.1.0/24 br1 metric 1

IPv4 192.168.122.0/24 virbr0 metric 1

I now want to the change the first row to something like

IPv4 default 10.0.0.1 via br0 metric 1

I can easily add a new route like that, but I can't delete the route from the first row.

And the gui has no possibility to change a route.

Or do I have to make another setting in order to get access to the internet via 10.0.0.0 ?

10.0.0.0 is my office network, 10.0.1.0 is my dmz network.

Some vms are attached to br0, some to br1.

What can I do?

Regards, Stephan