Pancho's right. It is fairly easy to kill all the moss using lawn sand or sulphate of iron (lawn sand is sulphate of iron plus sand) but unless you correct the conditions the moss will just come back. Moss likes damp so you need to ensure that the lawn is well drained, waterlogged ground will just grow moss. So drainage perhaps, aerate the lawn, lots of top dressing with coarse loam and so on. Then take Pancho's pub option. As an aside I once asked a golf course green keeper why I couldn't get my lawn to look like one of his greens. his reply was "you can, just mow the grass every day, scarify at least once a month, aerate a couple of times or more a year, top dress every autumn and use lots and lots of chemicals, plus make sure it is watered every day, but don't let it get too wet. And don't think about going away on holiday."