How do you lift a convertible top on a 1987 jaguar xjs by hand?

The procedure is covered in the Handbook:

Power Operated Hood - Manual Operation

In the event of a failure in the operation of the hood it is recommended that you contact your nearest Jaguar Dealer for assistance. If you are unable to contact a Jaguar Dealer the have a requirement to either raise or lower the hood the system is equipped with a manual control valve located on the body of the pump

NOTE: Due to the resistance of the hydraulic fluid in the operating rams some people may find it difficult to apply sufficient effort to fully manually raise or lower the hood.

To gain access to the control valve, remove the trim panel situated inside the rear storage compartment (use a coin to release the two slotted fasteners)

Turn the control valve clockwise to the position marked 'MANUAL'

WARNING: WHEN MOVING THE HOOD MANUALLY ENSURE THAT HANDS AND FINGERS ARE KEPT CLEAR OF THE HOOD LINKAGE

NOTE: The rear quarter Windows cannot be opened or closed manually, i.e. if hte hood is being closed manually the rear quarter Windows will remain in the open position.

To raise the hood:

Manually push the hood upwards from the rear and then pull it forwards until it is fully raised.

Press the button on the end of the hood handle and push the handle down. Engage the hook in the latch and then push the handle back into position. Repeat this procedure for the the other hood handle.

Turn the control valve anti-clockwise to the position marked 'ELECTRIC'

Slide the trim cover back into position and secure with the two slotted fasteners.