If you absolutely must remove the decal - if it actually is a decal - i.e., a sticker - you can try using a blow dryer to heat up the adhesive backing, which will re-activate the glue and make it tacky again while it is warm. Carefully lift and edge with a finger nail. I'm very good with an X-Acto and I can use the flat of the blade to start the lift, but I don't recommend that for anyone who doesn't use one every day. Don't try to remove it all at once: heat a little, lift a little, repeat, repeat, repeat. You can also try Bestine (rubber cement thinner, available at artist supply stores) as a solvent to remove remnants of the adhesive, which can otherwise be quite tedious to remove. Two cautions: (1) Be careful with the blow dryer; it can heat up the tube very fast and you can easily burn yourself quite badly. You might also damage the tube. (2) Most solvents - especially Bestine! - are highly flammable, so don't use it around open flames or even a running blow dryer. Solvents can also be absorbed through the skin and ultimately cause damage to the good old central nervous system, so wear gloves.

Or you could leave the original decal alone.