Replacing Battery (Correct method)
For those that do not have an Owners Handbook, the battery comes out via a door in the Front wheelarch. If the correct size battery is fitted, this is not a difficult job. If an over large battery is fitted, it can be more troublesome. The first time you do it, raise the car to high, fit the tyre changing prop, and remove the front wheel. Remove the battery door - you might want to take out each bolt, grease it & replace it before removing all together as preventitive maintenance. The correct battery come out no problem. If you have an over-height battery, then you may have work on the cross brace that has to be loosened on the outboard end then unscrewed from the access panel. It is actually the fender brace so don't discard it in a fit of anger. Plan on using some penetrating fluid on all threads before starting the project.
When you know what you are doing, and have the correct size battery, you can put the car on high, turn the steering all the way to the left, remove the ignition key, and the door and battery can be got at easily.
Replacing Battery (Alternate method)
(Anonymous) actually fitted a battery that could be dropped in from the top. It does require removing the voltage regulator and the hood latch, but that only takes a few minutes. Lifting the battery in and out from the top (with a battery handle) is much nicer. ****However, so many many people have destroyed their self levelling headlight control (which is no longer available and cost about 20 times the cost of the battery) that the time saving cost them dear. Don't do it. If you do some preventive maintenance by greasing the bolts on the battery door area, using the correct method is no great pain.