Hi Steve,
No problem, hairdryer is the tool you need. Just warm up small sections at a time. pick up an edge with your finger nail and ease away. On long sections just peel back as far as you have warmed, then warm a bit more and so on until the whole decal is remove. You will most probably get a dirty residue at the edges, just use methylated spirit to clean of then polish with good wax polish.
Tip when applying new one, get spray bottle full of water with a few drops of "Fairy Liquid" or similar in and throughly spray the area where you are fixing new decal. You can then quite easily slide into correct position, then use a squeege to smooth into place (for small areas just use edge of credit card). Next top tip........... now leave well alone until dry, peel off backing paper, Hey presto "Top Job".
Cheers
Graham F