I'm currently doing a project with IR sensor, but i don't know how to increase the range of the sensor. The attached picture is the circuit i'm using.

 

That's not going to work. The phototransistor has to provide an input to the op amp. You might want to read our full chapter on op amps, but here is a link on how to connect them and give voltage gain to the signal - http://www.allaboutcircuits.com/vol_3/chpt_8/5.html.

It is usual to pulse the IR transmitter at 38 KHz. Information is transmitted by varying the duration of 38 KHz pulse trains. You get better range with a signal at a frequency because you can make the receiver with a lot of gain at the signal frequency.

The LM324 is not a good op amp to work with. They are not nearly as good as modern designs like the LT1113.

 

It would help some of us if you would connect the dots [ or letters ] where possible, might add arrow to VR to show that it is a pot. Chech data on IR LED, pulsed , as suggested by beenthere, might give 10X current as oposed to average current. Use narrow beam IR LED.