I have this schematic for a 27mhz radio transmitter it just sends a signal that is then received and turns an led on when the button is pushed down. what I want to know is how do I change this circuit using the simplest method to change how much power is outputted. for example if I wanted more transmitting power what do I need to change or add and if I want less power what do I change or remove.

 

Reducing the output power is fairly simple and safe. Use an attenuator pad between the transmitter and the aerial.

Some caution may be required when increasing the output power. Depending on your jurisdiction, there will be regulations on output power, harmonics and spurious outputs.
You could increase the output power by a reasonable amount by increasing the supply voltage. To get a greater increase than is achievable that way you will need to add an extra power output stage.

 

Or just shorten the antenna, and probably increasing R7 and/or R2 will reduce output as well.

 

Raise or lower the battery voltage?

 

cut your antenna to match the output frequency. A mismatched antenna will reduce your range.
http://home.kendra.com/KJ7YL/ant.htm.

You can also look at products from mini-circuits if you want to add-on an RF amplifier. Use a spectrum analyzer to tune the frequency. http://www.minicircuits.com/products/Amplifiers_what_is_new.shtml Also, look at their application notes for stable RF design ideas.