It's a quick job to do - It is easier if you can get the back wheels on ramps or similar. Leave the car in gear and chock the wheels so the car cannot roll.
Start by removing the gaiter from the handbrake lever in the car. Slacken the 13mm nut under the lever, but don't let it come completely off, then drop the handbrake lever - that introduces slack into the cables.
Then under the car start at the front of the cables - remove the little plastic clip carefully and remove the ends of the cable from the yoke. The other end of the yoke has the nut on you slackened in the car.
Work down the length of the cable opening all the plastic clips and the hanger then remove the end of the cable off the back caliper.
In good old fashion, refit is the reverse of removal. If you can get some oil into the new cables it will help with lubrication and keep out the damp. When you are tightening up the nut on the handbrake lever to take in the slack, don't over tighten it or you will have the back brakes binding - about 6-7 clicks on the lever should be enough.
Biggest problem I had was the little brackets for the bolted hangers were badly rusted - I dropped the bracket off the car's frame, cut off the bolt head - replaced with a new bolt and refitted. Took about an hour to do the job and another with all the faffing about.