So I have to start all over to the CSS lessons?

Yeah, just click the switch button under the track you want to switch to on the tracks page (https://teamtreehouse.com/tracks)

I have the same problem. I'm four months into my Treehouse studies; I've completed HTML, CSS, Intro to Programming, and I was well into JavaScript. When I was given the option to update to the new CSS and JavaScript sections, I chose to do so. I read everything carefully, but I still did not realize that all of the progress I had made before (except HTML) would be erased, and I would have to start over with CSS from the beginning, as if I had just completed HTML!

I did see the warning that "current progress may be subject to change depending on the types of updates made to your Track." However, for some reason I thought this meant I might have to watch a few of the CSS, Programming, and JavaScript lessons again, and/or complete a few quizzes over again. I thought that review would be good for me, so I chose to update. I thought this would be added on to the progress I'd already made. I didn't think it meant that almost ALL my previous progress would simply disappear, as if I'd never done it.

I wrote to support and suggested that they word that warning a little more strongly - something like "Consider this carefully, as there is a possibility that you may have to entirely re-do some of your previously completed courses over from the beginning!"

If I have to start over from the beginning of CSS again - and based on what 64yes wrote above, it sounds like I am - then my Track completion is going to be significantly delayed, which saddens me greatly because I've invested a lot of time in this. But if I have no choice now but to start over, I suppose I'll console myself by reminding myself that once I've finished the coursework for the SECOND time, I'll know the material much better, and therefore be that much more prepared for a web dev job.