what are you trying to achieve?
if you need a point-to-point radio link, there are some options with directional antenna.
but for clients on a floor it most likely comes down to adding access-points for coverage.
in addition to this
you may change the power level, but there is a legal maximum transmit level.
You can concentrate radio signal in certain direction with special antennae, but this also has restrictions to the max transmit level.
for higher levels it may not fall under the wi-fi regulations, you may need to request a license,
