Range extending would only be of any use with a more directional and external antenna.
If your ESP does not have an external connector of any description then you should avoid hacking it as you may cause unwanted interference to other devices and possibly kill the TX section of the ESP with a bad SWR.
Buy one that does have the external connector would be my advice as you can then buy OFF THE SHELF antennas for testing the range / direction.
As pointed out by srnet you are getting into an area of the radio spectrum where antenna design can be super critical and may need quite specialised equipment to test / set up an antenna.
If you don't know what SWR means then it is doubtful you are ready to play with antennas !

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