Well, you could download the new SDL2 based version and replace the existing one. Since it's better to unpack the archive on the Linux system, you can run from the terminal
wget http://spatula-city.org/~im14u2c/intv/dl/jzintv-20200712-linux-rpi-sdl2.zip
sudo mc /opt/retropie/emulators/jzintv
This will download the new version and open up MC with the location of the existing jzintv version on the left pane. On the right pane, browse for the .zip file you downloaded and then just press Enter over the selected file, you'll see the contents of the archive and you'd be able to copy the new jzintv binary over to the left.