How to back out of an accepted offer?

[VoidInColor]

I was waitlisted by my first choice school and accepted to my safety school. I accepted my safety school's offer on the 15th, and today (17th) they sent me the GRA contract. I have not signed it yet, since I wanted to check with my first choice to confirm that there was not a slot for me. However, after everyone had ended up choosing where they wanted to go, the internal fellowship I was waitlisted for at my first choice had open slots. Since they got more funding, I've been accepted to my first choice. I haven't signed anything for the safety school or put down any deposit, just sent an email saying I'm attending. How do I go about telling my safety school that I'm no longer attending? Do I just thank them and vaguely refer to changing plans? I'd like to do this as politely as possible.

[limonchello]

Your school will understand, especially if you're apologetic and explain that this couldn't be avoided. I think I've seen some posts around explaining how people went about explaining it, but I would write up a nice email explaining what has happened, that you'll be accepting the other offer (don't really need an explanation, but you could say more funding etc) and then ask them to 'release' you.  Congrats!