the easiest thing to get hold of (and the least dangerous to work with) is acetone free nail varnish remover. you can pick it up in just about any chemist. its not strong enough to 'strip' paint, you will need to do a little bit of scrubbing with a toothbrush, but it doesn't give off huge amounts of unpleasant fumes or burn the skin. and its also gentle enough to use on plastic miniatures. it will also soften superglue and occasionally weaken the joins created by polystyrene cement. but that shouldn't be an issue if you are planning on re-painting the miniature anyway.