Easy Peasy Mate
Inside the boot(on left and right hand sides) you will see a dark grey plastic cover, kind of oblong in shape. At the top is a locking catch, turn the screw 1/2 a turn, don't even need a screw driver, a key will do. This will enable the cover to be removed.
Then you are at the rear of the light cluster, two plastic bolts which you can remove by hand. Then you can pull the cluster out getting access to the bulbs.
It's a 2 minute job, no tools needed.
(P.S. The brake light is the top one)
Steve.