Silicone caulk is a material that is used to seal up an area from either air or moisture. Over time, the silicone caulk can become worn, mouldy or cracked. If this happened, the caulk will no longer be an effective sealant for your home. You will need to remove the silicone caulk and reapply it. You can remove much of it manually by scraping, but some of the hardened silicone caulk will likely need to be dissolved before you can get it off the surface it's adhered to.
Make tiny cuts in the hardened silicone caulk with a razor blade.
Use your hands or pliers to remove chunks of the hardened silicone caulk from the area.
Scrape away what you can using a glass scraper. Be extremely careful that you do not scrape against the surface the caulk is adhered to. It can cause damage.
Apply white spirit to the hardened silicone caulk that you cannot remove by hand. Use a generous amount to be sure you dissolve all the silicone caulk.
Wait several minutes. Continue reapplying white spirit if the area starts to dry.
Scrub the dissolved silicone caulk with an abrasive pad to remove it completely from the surface.