The best way to do that is to delete the build folder for the package. Usually that is build/<package_name>. However, the package places generated files in the devel folder, and those are not as easily cleared out because they are mixed in with the generated files from other packages. The most sure fire way is to delete the devel folder and the build folder, but deleting just the build/<package_name> folder and the devel folder might still work and be faster.