How do I delete a local repository in git?

In the repository directory you remove the directory named .git and that's all :). On Un*x it is hidden, so you might not see it from file browser, but

cd repository-path/
rm -r .git

should do the trick.

Delete the .git directory in the root-directory of your repository if you only want to delete the git-related information (branches, versions).

If you want to delete everything (git-data, code, etc), just delete the whole directory.

.git directories are hidden by default, so you'll need to be able to view hidden files to delete it.

To piggyback on rkj's answer, to avoid endless prompts (and force the command recursively), enter the following into the command line, within the project folder:

$ rm -rf .git

Or to delete .gitignore and .gitmodules if any (via @aragaer):

$ rm -rf .git*

Then from the same ex-repository folder, to see if hidden folder .git is still there:

$ ls -lah

If it's not, then congratulations, you've deleted your local git repo, but not a remote one if you had it. You can delete GitHub repo on their site (github.com).

To view hidden folders in Finder (Mac OS X) execute these two commands in your terminal window:

defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder

Source: http://lifehacker.com/188892/show-hidden-files-in-finder.