1. Remove the submodule entry from .git/config
git submodule deinit -f path/to/submodule
2. Remove the submodule directory from the superproject's .git/modules directory
rm -rf .git/modules/path/to/submodule
3. Remove the entry in .gitmodules and remove the submodule directory located at path/to/submodule
git rm -f path/to/submodule
For more information please go through the following tutorial to get more info about git: