Tom, remove the bottom cushion from the starboard berth and you'll see slide bolts on each end of the berth . Disengage the bolts and then gently slide the berth top out towards the center line of the boat. When it's all the way out you'll be able to engage the slide bolts to secure the berth in its open position. Put the cushion back in place, then slide in the extra cushion, which is skinney and covers the extra berth width.
The water tank and a small storage compartment are beneath the starboard berth top. You can access them by disengaging the slide bolts and then tilting up the berth top, lifting it from the inboard side. Take care in doing this as it's easy to gouge the teak on the bulkhead while performing this akward maneuver.
I like my '85 E26 a lot, but wish Ericson had resisted the urge to design the interior in a way that they could could advertise, "sleeps six", and instead put in more storage space.
I've done quite a bit of work and minor upgrades on my boat. Feel free to email me if there's anything you think I might be able to advise you about.
Fair Winds!
Captain Don
Gitana