Promoting a release with different variables

I have a release that has been deployed to our testing server successfully. However when I try to promote this to a different environment , I am unable to update the variables that I set prior to me making the original release.
I have read about changing variables here :
It doesn’t look like there is an "update variable " link just yet ?

Are you sure you want to be doing this?

If your variables differ between environments (eg database connection strings), you simply pick different ones for each environment on the Variables screen. Define one version for the Testing environment, the other for Staging, and another for Production, etc.