So I have been doing the C25K for about a month now. I did week 1 for 2.5 weeks then advanced to week 2. I have ran on session 2 for almost 2 weeks now. I am able to run it with out looking at the timer most of the time. I feel like I can advance but I am concerned about my legs. While I am walking in the cool down my legs feel like Jello. Should I try advancing or wait until my legs don't feel like Jello?

I think you should keep going. However, keep in mind that you should do whatever makes you feel comfortable.

Personally, every time I was able to finish a workout, I moved on to the next day's workout. Any time it got hard, I reminded myself that it's not meant to be a cakewalk; it's SUPPOSED to be a little challenging.

I would keep going. I had some jello legs in the beginning, but eventually my legs got used to it. Stretching helps a bit, too.

If your legs or muscles are actually hurting, that's another story. Do what feels right for your body. Generally, as long as I was able to finish one day, I'd try the next one.