Hi Giahosa,
First thing : Smoke from a breaker is NOT good. The lug on your breaker for the red lead seems all burnt. Close your breaker in your main panel and replace your GFI breaker. Assure that your red, white and black lead are correctly torqued in the breaker, a loose connection can lead to a fire. Check also the connection in your spa to assure that everything is tight. If the breaker trips again after replacing the gfci, you'll need to check the amperage of the spa and use a megger to check if the heater is "leaking to ground".
Hope this helps