You will have to have a contractor check your foundation, your joists, every thing that holds the house up now if the waight span can hold it, then you have to see if anyone will give you permits to do so if you do have the correct muscle that the house has to do what you want.
Most likely you can go up, its cheaper then going out. However you will find you will need to replace all of the ceiling joists with new floor joists that are larger. Some interior walls will need to become structural in order to support the loads of the new rooms above, and some additional foundation work may be required, depending upon the load profile that must be carried down to the footings of the home.
A structural engineer or architect will be required to draw up the prints and stamp them for approval from the local municipality in which the home is located.