Change Default Bank Account?

Hi, I have 2 main bank accounts, an OLD bank account - no longer used and a NEW bank account which is active. The old bank account is 1200The new bank account is 1205. Unless every time I open Sage I choose Modules -> Bank and select 1205, then 1200 is chosen and soemtimes I enter a transaction into the wrong bank account. I have tried to delete the 1200 in a new comapny I recently opened but I'm not allowed, as it is the 'default' bank account. Does anyone know a way or is there a setting to make the default bank account 1205 ? Thanks