How do I detach the mine carts?

I want to use the cart on the left for a mech build I'm putting together. How do I detach it from the cart on the right? If that's not possible, is there an unconnected cart with the cage somewhere else? Thanks!!

I want to use the cart on the left for a mech build I'm putting together. How do I detach it from the cart on the right? If that's not possible, is there an unconnected cart with the cage somewhere else? Thanks!!