This is an old school dipole antenna that needs to be soldered on to your VTX.
Modifying the antenna is pretty easy.
First, de-solder the current antenna from the vtx. Take a look at how it's held on in three places - there are two outside connections which are the ground (soldered to the same pad on either side) and there is a single lower connection.
Now we'll make the upgrade antenna look like that. First cut your antenna about this short. If you want a little room to make mistakes, go a couple millimeters longer.
Gently remove the outermost translucent material to expose the woven ground wire.
Once the outermost translucent layer is removed, slowley pull apart the woven ground wire and twist it into the two outside connections. As you'll see these will need to be a bit shorter than the central wire. Remove a bit of the white insulation between the core wire and the woven ground wire so that it looks like this.
Now just solder the central wire to the lower pad and the two ground twists to the ground pad. Easy as pie!! Just make sure they're not touching in any place and you should be good.