There should be a tiny grub screw at the back iof the tap body, remove this and the spout will come out. Replace the rubber "O" ring/s, smear the new "O" ring with vaselene, not too much, but this will assist you when putting the spout back in. Whatever you do, DO NOT drop the grub screw down the sink, and do not overtighten it when you put it back.
Richard
October 2012