These small two-way radios are deliberately made so you cannot add a better antenna. That’s why they don’t need a license, and the FCC is happy because they cannot get out very far and cause much interference to other radio users. If you modify the radio in any way, even if you were a technician and could do it properly, then it would no longer be an “approved” radio for use without a license. You would be breaking the terms of the no-license class of that radio, and you could be fined. And if you don’t know what you are doing and you try to modify the antenna, you will change the frequency that it is tuned for… and that can damage the transmitter.