Pull the slide back toward the retracted position as far as it will go (it's vital to get it all the way back), then pry the nose up with a stiff putty knife. Do this carefully, because the spring will go bye bye very easily when the thing flies apart.
It takes sort of a leap of faith to disassemble one the first time. They feel like they will break before coming apart, but they're apparently made of some pretty sturdy stuff.
My '74 Argosy uses the same latch with a flush pull on the interior doors. For those, you have to take the pull off first to get the latch to retract all the way.