Howw does one switch to 3-4-4,3-3-5, etc?

In general, your head coach determines whether your defensive playbook is geared toward 3-4 or 4-3. Your defense will automatically adjust your secondary to goal line, nickel, dime, etc. based on the offensive personnel (as long as you have plays in your gameplan that match). If you want more control, you can set rules under the gameplanning-> rules section.