The access is the same as for changing spark plugs.
The testing method is as above, but also make sure that the HT leads are insulated and tucked safely away from any part of the body to avoid a spark.
The easiest is a compression tester that has a screw fitting as opposed to a rubber cone, the screw fitting allows you to do this test yourself without the need for a helper.
(With the rubber cone type, you can still short-circuit the starter motor and do this as a one-man job, but on automatic cars this can be risky because the starter motor short-circuit method by-passes the gear selecor inhibitor so the car could be started in gear by mistake - though obviosuly not while while the plugs are out)
Then carry-out a dry and wet test on any low-compression cylinder by adding a couple of spoonful of engine oil through the spark plug hole - if the problem is due to compression rings' wear, the oil will boost the compression on re-testing, if the low compression is due to leaky valves (or HG) then the added oil will have no effect on the compression which will remain low on the re-testing.