How to remove the valve?

I’m about to take the plunge and order some Radioator valves but I’d like to check compatibility first. I’m scared to remove the valve. When I start to unscrew it the silver bit at the bottom starts to move too - is this correct?
Photo on the Dropbox link.
https://www.dropbox.com/s/vp03rx3mp82jry6/IMG_1307.jpg?dl=0
Many thanks
Ashley
Photo on the Dropbox link.
https://www.dropbox.com/s/vp03rx3mp82jry6/IMG_1307.jpg?dl=0
Many thanks
Ashley
0
Answers
I should clarified that I mean the silver ring immediately below the Grey part. Not the very bottom.
@Ashley Yep you should be unscrewing it by the silver ring. Unscrewing that should reveal a pin which is pushed down or released by the 'grey part' to be replaced by the tado thermostat.
@Ashley You should unscrew the silver ring.