I struggled for a long while to perfect the art of replacing drum shoes. Fortunately, they should last at least 40,000 miles as long as you don't live in a hilly area! Remember, if you get stuck, have a look at the other side. This is where a trolley jack comes in handy so you can have both wheels off at the same time.
With the rear wheel removed, the first problem is to remove the brake drum. In theory, it should just pull off but in practice they may need a bit of a tap with a wooden hammer. Mine have always been very easy to get off as long as I remember to take the hand-brake off first! With the drum off, the brake shoes are visible. In the centre of each shoe is a spring loaded fixing pin which requires a special tool to release. However, all you actually need to do is grab it with a pair of pliers and push down on the spring.
As you push, rotate the pliers so that the slot on the pin and spring match. Release and the assembly will come apart.
Repeat this for the other shoe, and then grab both shoes and slowly pull them towards you. They will be pulled together by the retaining springs and hopefully shoes and springs will come away from the back plate. Now is the time to pray that you can put it all back together! Wipe the whole area with methylated spirit making sure to remove all traces of brake dust. There are certain raised areas of the back plate where the shoes rest. I recommend for a professional finish that you smear these with a small amount of copper grease.
Now before attempting to put anything back, I suggest that you get the two new shoes and orient them correctly on the floor. There are two long retaining springs which are extremely strong. One goes at the top of the shoes and the other at the bottom. Make sure you know which is which. I prefer to leave the springs until last but I have seen people do it differently. Place each shoe in place so that the base fits in its slot at the bottom, and the top of the shoe fits into the slot on the side of the small cylindrical brake piston. One minor complication here is that you also have to attach each shoe to the hand-brake mechanism. With a bit of juggling about, the apparatus should fit together. Don't worry about the ratchet mechanism. That is activated by the hand brake and will set itself automatically.
With the brake shoes in position, re-fit the spring loaded clips by once again compressing the spring with a pair of pliers and then twisting until it locks in place. This can be a bit tricky especially as you've got several other things to hold in place as well. Once they are fitted you can let go and the shoes should stay put.
All that remains is the difficult task of re-fitting the two retaining springs. This can be very frustrating. The easiest way I have found is to use a small screwdriver. Fit ono end of the spring and place the tip of the screwdriver in the other hole (the target hole). Lower the screwdriver and wrap the free end of the spring around it. Now raise the screwdriver slowly so that the spring slides down towards the target. You will be able to get very close this way, but the final fixing in place should be done with a second screwdriver to push the spring clip into the hole. This method usually works first time. With both springs in place we are almost finished. Check against the other side to make sure you've not done something silly. I also suggest you slide the shoes around a bit to get everything looking aligned.
Before you fix the drum back on, you will have to push the brake piston closed to allow for the larger thickness of friction material. It may be a tight fit getting the drum back on. Make sure there is no burr on the side of the drum. If there is, you could try grinding this down a bit to ease the problem. When both wheels are on again, you should pull the hand-brake on and off a few times to allow the adjusters to move and tighten up the shoes onto the drum.
One footnote here: you can strip and clean the brake pistons which I have found improves braking no end. Remove the gaiters from each end of the brake piston. With a rag in place to catch the fluid, gently pull out the pistons and catch the spring in the middle. They are very simple devices. Check the condition of the rubber seals and piston walls. If they are frayed or cracked then you should replace them. Pass a rag through the open cylinder and make sure everywhere is clean. Clean the pistons, rubber seals and gaiters, and then place a small amount of brake fluid on the seal before pushing them back into the cylinder. Make sure that the spring is put back. Refit the gaiters over each end. Don't forget to bleed the brakes after you have finished refitting the shoes.