Repair the floor, there are ways to keep in place, or cracks in the floor from time to time, you will need to replace split or broken. Results of inspection and repair, as should be done under the subfloor, the slab must pay sometimes. To do this it is possible to use a flooring specialist, moderately experienced owners, do your work.
Lower?
The first thing homeowners is to find something under the floor before you start work. For all kinds of pipes and electrical cables in the ground will be moved out of the way and work. Then, the floor slab to be removed depends on how it was intended.