Increasing the range of an IR based detector
If you provide the part numbers for the IR LED and receiver we can probably provide a more concrete plan to increase the range, but in more general terms:

The two ways I can think of to increase the range involve increasing the output of the LED or increasing the sensitivity of the receiver. The latter I forgot about until George Herold commented about increasing the gain.

So on the receiver end you can increase the gain. The one thing to be careful of here is making sure it still filters out any noise from external IR sources. If you can access the 38kHz pulse, then like George mentioned in the comments, you can use that for lockin detection.

On the LED side the main option is to make sure it is at it's max output. You want to max out the current going through it, and you can utilize a lower duty cycle to increase the current through the LED past it's rating. You could also simply use a higher output LED, the range you're getting seems very low to me so examining the parts you're using might be a good idea.