Just delete the whole directory. This will delete all the projects but also the Eclipse cache and settings for the workspace. These are kept in the .metadata folder of an Eclipse workspace. Note that you can configure Eclipse to use project folders that are outside the workspace folder as well, so you may want to verify the location of each of the projects.

You can remove the workspace from the suggested workspaces by going into the General/Startup and Shutdown/Workspaces section of the preferences (via Preferences > General > Startup & Shudown > Workspaces > [Remove] ). Note that this does not remove the files itself. For old versions of Eclipse you will need to edit the org.eclipse.ui.ide.prefs file in the configuration/.settings directory under your installation directory (or in ~/.eclipse on Unix, IIRC).

Undo a commit & redo

$ git commit -m "Something terribly misguided" # (0: Your Accident)
$ git reset HEAD~                              # (1)
[ edit files as necessary ]                    # (2)
$ git add .                                    # (3)
$ git commit -c ORIG_HEAD                      # (4)

1. This command is responsible for the undo. It will undo your last commit while leaving your working tree (the state of your files on disk) untouched. You'll need to add them again before you can commit them again).

2. Make corrections to working tree files.

3. git add anything that you want to include in your new commit.

4. Commit the changes, reusing the old commit message. reset copied the old head to .git/ORIG_HEAD; commit with -c ORIG_HEAD will open an editor, which initially contains the log message from the old commit and allows you to edit it. If you do not need to edit the message, you could use the -C option.

Alternatively, to edit the previous commit (or just its commit message), commit --amend will add changes within the current index to the previous commit.

To remove (not revert) a commit that has been pushed to the server, rewriting history with git push origin master --force is necessary.

Further Reading

How can I move HEAD back to a previous location? (Detached head) & Undo commits

The above answer will show you git reflog, which you can use to determine the SHA-1 for the commit to which you wish to revert. Once you have this value, use the sequence of commands as explained above.

HEAD~ is the same as HEAD~1. The article What is the HEAD in git? is helpful if you want to uncommit multiple commits.