I believe you mean wanting to exchange your CPs for a ship.
In that case, the reason you do not see an option to do such is because you are not planetside. You have to be on a planet, outside of your ship or any other entity, in the open, in order to exchange your CPs for a ship.
In, however, the case that you do mean getting a custom image for your ship, in order to get the ID Number of your ship, the best way to do it is look at your ship inventory and hover your mouse over the checkbox that is left of the display of your ship.
____________Time to go to war with the Flame Tigers