Please help me with routing problem

My whole network runs on 192.168.3.0/24 network and my gateway was 192.168.3.254
now recently I got an new ADSL router with an static address 196.214.186.x
I cannot get my routing solved, my RB that is connected to the gateway 192.168.3.254 is 192.168.3.90

Where must i start?

If you want to change default gateway,
- add IP address on public interface;
- add new default gateway (delete previous one);
- change NAT masquerade rule to new outgoing interface (if it changed).