http://www.hollographics.com/info/ap....html#cutvinyl
try this sir
small amount of soapy water makes life very easy, individual letters if going over existing just float them on one by one, failing that get a low tak masking tape, apply over letters, peal of backing paper and apply as one ensure squeegee'd down as req carefully peel away masking tape, ~~(application tape normally is applied at point of sale)
enjoy best done in warm conditions