Not to bad to change this, but you do have to take the wheel off to do it. Managed to get a pump off ebay for £4.50 so cheap enough.
Right, take the wheel off and make sure you use a decent jack as you will have to lean under the car to get some screws!
Remove 5 self tapping screws from the back of the arch liner, 2 on the bottom and 3 on the inside. There are also 3 little plastic pop rivets up the outside edge of the wheel arch.
Bend the liner and rest on the hub:
Now you can see the washer tank, the middle pump is the windscreen one. Twist is anti-clockwise and pull off the tube and lift out of the tank. Push the new one in and connect the plug and tube:
Put it back together the way you took it apart and there you go