Amending EXISTING Engage Template Colours

Hi,

I changed a (default) Engage template colour scheme, and saved it as NEWSCHEME. I now want to make further colour amendments...

How do I do this, as it only seems to let me do it IF once changed, I save it as ANOTHER (new) name, which I do not want to do.

I suspect I have accidentally pressed my own "dumb button" here - but my head has exploded from trying things - there must be a simple way to do this (?).

Thanks!

Bruce