How many times a week should I do a hard workout?

As a general rule, most fitness experts say don't work out hard more than three times a week. Of course, what is "hard" is highly individual and refers to whatever level of effort elevates your heart rate, brings on a slight sweat, and deepens your breathing. If you're prone to injuries, three "hard" workouts a week may be excessive, at least for the first several weeks, until your body becomes accustomed to the effort; there's good evidence that the risk of injury increases as you work out hard more than three times a week. If you're cross-training, however, you'll have more latitude in this regard if you alternate activities that work the upper and lower body.

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Much of this will depend on your current fitness level.  If you are just beginning exercise then each session may be a challenge.  If you are fairly active then you may be able to complete up to 3 hard workouts per week.  You must first figure out your fitness level and decide from there.  A good suggestion would be to complete 1 to 3 hard workouts per week.