How do I upgrade roads on simcity 5 without destroying the existing road and all the buildings on it?

Maybe you are wondering how to upgrade a Street into an Avenue without having to bulldoze everything in the area?  

The answer is you can't.  This is one I have been struggling with, because the optimal zoning between a Street and Avenue is different.  I am guessing that once you hit the stage where you need the Avenues, you have to raze a section at a time?

I saw a tutorial where he started with Avenues, and I tried for myself.  Of course I had to take out all 3 bonds, but it worked out, however I worked out.