Well the head must be removed from the car. It will require special tools. The head needs to be stripped and valves removed. The old seals must be pressed out and the new ones pressed in.
First remove the cams. Valve springs in the cyclinder should be removed. C- clamped overhead valve spring compressor is needed. Do not use compressor that is having springs in head.
Once you have to check whether it is working or Not proper. and then check the existing valve, and we can replace the valve steam. When it replace please connect proper.