No reason why you shouldn't try this yourself - however, just a point or two. There will be a shut off valve either side of the pump. These may be seized up, or maybe could leak when you touch them. If in doubt I would simply depressurise the system before straining anything. Sometimes the nuts on the pump itself are so large its impossible to get a spanner in - or at least not enough room to turn it. Finally, make sure you get new washers with the new pump.
John, December 2007