can i bulk up working out 4 days a week? 2 upper body days and 2 lower body days?

Answer 1

It would be better if you did a 3 day full body work out as opposed to only 2 days on each muscle group a week. 3 alternate days a week is optimal for beginner to somewhat advanced lifters.

Answer 2

bulking up or increasing muscle mass is 80% diet, training only provides the neccessary stimulus to the muscles and to the central nervous system. so the diet that you follow and the intensity of training ultimately determines the size of your muscles not simply the frequency of training.

4 days of weight training a week is sufficient if you have a properly designed diet and training program