Strength training - how often should I change the DVD I use??

[mandy miller]

Hi there

I am currently doing STS, but I have other weight lifting DVDs (Gym Style, Slow & Heavy & Pure Strength for eg) I like these DVDs because I like to work seperate body parts on alternate days

My question is, how often should I change the DVD series? For eg if I´m doing Gym Style (1) legs (2) Chest & Tri (3) Bk, Bis, shoul should I do this for a week, a month before moving on to say Slow & Heavy?

Any tips would be appreciated. I don´t want to move on too soon, but then I am aware about muscle confusion

Thanks!