Whether your guitar's rosette is worn or simply not to your tastes, an adhesive rosette can be exchanged for something closer to your style. This is a slow process, though, and should not be attempted in a hurry. However, if your rosette is inlaid and varnished over, do not attempt to change it. Instead, apply a new adhesive rosette over the top to cover the existing design without tearing off the finish of your guitar.
Unstring the guitar so that nothing obstructs the guitar's sound hole. Ensure that there is no water in the iron's steamer, and turn it onto its lowest heat setting. Cover the sound hole with your towel.
Place the iron on top of the towel, and allow it to gently heat the rosette's adhesive. Allow it to sit for one to two minutes, checking on the guitar regularly.
Test the adhesive by sliding a needle between the rosette and the guitar. If the rosette does not peel up easily, replace the towel and iron, and heat the surface for another minute.
Thread the needle with a length of nylon thread and slide the needle between the rosette and guitar once more. Push the needle all the way through until you can grab hold of the nylon thread at both ends.
Pull the thread toward you, separating the rosette further from the guitar. Continue to do this until you have made a complete circle around the sound hole, thus separating the two. Using thread allows the guitar's finish to remain intact rather than scratching along the surface with a metal instrument.
Remove any lingering adhesive with a gentle solvent such as naphtha. Keep the solvent isolated to the area with the adhesive.
Measure your rosette's available space before selecting a new rosette and, once you have acquired the rosette, slide it into place before using any adhesive. When you are sure that it fits your guitar, place the new rosette around the guitar's sound hole with the adhesive side down and gently press it into place.