It's not an easy job, but its far easier than other rear discs I've worked on. The main
problem is pushing back the brake pistons, I just don't see how you can do it without the proper tool to wind them back in. There was mention of people using a pair of pliers with mixed success, but for the sake of £21 get yourself to Halfords and get the tool.;
http://www.halfords.com/webapp/wcs/..._productId_214227_langId_-1_categoryId_165469
Once you have that, here are the steps;
1. Undo the bolts holding the caliper on.
2. Undo the bolts holding the caliper bracket on.
3. Undo the disc retaining screw.
4. Swap the discs over.
5. Remove the pad retaining spring and pads.
6. Wind back the piston.
7. Fit the new pads and retaining spring.
8. Fit the caliper bracket.
9. Fit the caliper.
10. Operate the brake a few times to get the piston in place.
11. Check the handbrake.
12. Repeat on the other wheel.
I'm assuming you have replacement pads as well as discs? You don't want to leave old pads on new discs.
I think it took me half an hour per wheel for the rears, twenty minutes of which was getting the pistons rewound. The fronts were exactly the same as virtually any other car, and they were about fifteen minutes each.