Remove old window caulk with a putty knife, utility knife or razor blade. Regardless of the tool you choose, the method is virtually the same. Wedge the blade of the knife between the bead of caulk and the window or window sill, and scrape the caulk loose.
Prior to removing the old caulk, put on a pair of gloves to protect your hands from the sharp blade and to prevent the development of blisters. Cleaning the area also helps identify the interface between the caulk and the window, which reduces the likelihood of inadvertently removing paint from the window sill. Applying caulk remover softens the caulk, making it easier to remove, but the softening process typically takes two hours or more.
Once the caulk has sufficiently softened, simply push the knife or razor underneath the caulk, and scrape off the caulk. A razor blade is particularly useful for removing stubborn caulk from corners and from the window panes. Scrape with a razor blade toward the outside edge of the pane, and remove any remaining caulk using a cotton ball or rag dampened with rubbing alcohol. After removing all of the caulk, wipe down the window and sill with a damp rag to remove any loose caulk debris.