How to replace windscreen washer pump on clio (1999)?

The windscreen washer pumps water on the first use. If I use it again the pump makes a whirring noise and only pumps a dribble from the nozzles. If I leave it for a while it pumps on full power then repeats the dribble on second use. Does the pump need replacing??? How can it be got our from the position under the windscreeen wiper blade.????? Reg