I want to know how I can increase the transmitted power for the infrared transmitter.
You need to tell us what transmitter and receiver you are using and how the transmitter is driven.
You can increase the current through the transmitter, as long as you do not exceed the maximum average current for the device.
Or you can transmit pulses from the transmitter, to get more peak power, but still keep average power low. Again, check the specification for your transmitter to be sure not to exceed the maximum instantaneous current.
Or you could focus the transmitted light to give a more directional beam.
Or modulating the light (typically with about 38KHz) will give better reception with the same transmitter power, since extraneous IR sources such as sunlight tend to get filtered out.
Or use multiple transmitters......