Should I decrease my carbs after training?

What is your aim for dropping the carbs after your workout?
Post workout, the body is beginning to produce cortisol, which is detrimental to the body. Insulin will inhibit this & consuming simple carbs is a quick & easy (pardon the pun) way to cause this insulin response. Another way to do this is using the amino acids glycine & glutamine. This is something advised by biosignature practitioners to those that are carb sensitive.
You could drop the carbs from the pre-workout shake & consume a protein shake during your workout if you are just looking to consume less carbs overall.

Hi Paul,

Assuming your goal is to lose fat, you don't need the pre-workout carbs as you will adapt to training with lower carbs and you should still be able to train effectively although you may fatigue earlier in the workout than if you had more carbs in your system. Much of this depends upon how drastically you are cutting your carbs. If you are getting 150 - 200 grams of carbs per day, it shouldn't affect your weight training once you become accustomed to this level of intake. Lower levels can affect training volume and endurance but it affects different people differently.

Keep taking your post-workout carbs and don't cut them unless you've cut virtually all other carbs and bad fats from your diet.