On a ficus plant, leaves and new branches can grow out of the side of virtually any live wood surface; even from older, "hardened" wood. New growth from the bottom is normal, particularly after any kind of shock which will cause all sorts of new growth. But if that top part is alive, you should be seeing new growth coming from the top, too.
Check the tips of the top branches. You should see small, green, needle-like buds that are the growing tips of those branches. If they look brown or are absent, those top branches may be dead. You can check by cutting a branch or scraping with your fingernail the outer layer of a small branch to see if you can detect any green. If there's no green, it's dead. If it's dead, it will become brittle soon enough.
Assuming the top branches are still alive, there's nothing you can really do to favor new growth up there. Just maintain favorable growing conditions to promote good general growth overall.
If those branches have died, you basically now have a ficus bush. Don't panic. It will probably do fine. It will just have a different growth habit (In Southern Florida, it's actually quite common to see thick, lush Ficus hedges).
If you want to encourage a more "tree-like" growth from what you have left, pick a few of the strongest, most upright branches coming from the bottom of the tree and cut off the rest. Given enough time and growth, you'll eventually end up with an attractive, now-multi-trunk tree again. As those multi-trunks become thicker and thicker, they'll actually start merging together, which is actually a rather attractive.
Just as a side note, ficus trees will drop leaves for a bazillion apparently-innocuous reasons. The leaves of a ficus tree are non-phototropic, meaning they can't turn towards the light. So, if you move or turn the plant, it has to drop leaves and regrow them to adjust. If the temperature changes, they'll drop leaves. If watering conditions change, they'll drop leaves. Draft? Drop leaves. Kick the side of the pot, they'll drop leaves. It's nothing to worry about; This is completely normal.
Don't panic and water more when leaves start dropping. That's the opposite of what you want. Always water thoroughly but only after the surface has completely dried out. Light on the fertilizer and only when leaves are actively growing.