On mine, you have to lift up and pull out on the front board. It has little wedges on the underside that keep it locked into the couch position.
If that doesn't work, you may need to loosen some screws: remove the cushions, unscrew the plywood & remove it, and under it you'll have 3 long screws that go into the sliders (at the front trim board area)- these screws, if too tight, won't allow you to lift up slightly to pull out the bed. So try loosening them, then lift and pull out.
Hope this helps!
"If you want something done right, do it yourself!"