Here's a video we have on our website that shows how to remove the car seat -

If you have a Stomp with a Galaxy car seat (Red Buttons on each side of the car seat) this is removed using the memory clips on your adapters. The adapters are to stay in your car seat at all times, including when on the isofix base. The black memory clip needs to be pushed towards the handle of your pram. This will hold the stay unlocked for you to do the other side safely and conveniently. Once unlocked, the car seat can then be lifted from the chassis. 

If you have a Stomp with a Mercury car seat (I-size) The adapters need to remain on the chassis at all times. The handle of the car seat will need to be in the upright position to be unlocked from the adapters (Back behind the hood to be locked). This can then be simply lifted from the chassis.