How often should I change workout routines?

[PACKERBACKER_1111]

I've been working out for about a year and a half. I did grow a bit but I hit a plateau. I've increased the weight I lift and I try to do different types of workouts according to magazines but they don't say how long to keep doing the excercises.

I'm currently doing a chest workout, I've been doing it for a month now, is it time to change to a different routine for the chest?

Can someone give me some tips? Or where can I look to find some good workout routines?

Thanks!!!