Confused about UCAS decision changes.

you are able to change a choice as long as it is within the 7 day period of you entering your decisions online not once you get the confirmation letter

Hello,

Sorry if this thread has been done a million times, but I've been doing some research about changing my UCAS decision but it has left me a bit confused.

Here's the context: I firmed Leeds and put Reading as my insurance on 1st May. Earlier today I was having doubts about Reading as my insurance and now I think I'd like to change it to another one of my offers that I 'declined' in the UCAS track system.

Am I able to ring UCAS to ask them to change my insurance to Exeter, for example, even though I declined their offer in UCAS?

Also, this 7 day period of being able to change offers; is this after the date of sending out a confirmation letter to your house, or after making your decisions online?

Any help would be greatly appreciated! Merci.