Force.com IDE Developer Guide

Force.com IDE UI Overview
Getting Started with the Force.com IDE
Developing with the Force.com IDE
Testing Code with the Force.com IDE
Deploying Code with the Force.com IDE
Getting Started with the Apex Debugger
Summary of Getting Started with the Apex Debugger
Set Up the Apex Debugger
Explore a Simple Debugging Puzzle
Apex Debugger Limits and Considerations
Apex Debugger Troubleshooting
Relaunch Your Debug Configuration
Kill an Orphaned Session
Kill a Debugging Session in Setup
Kill a Debugging Session with the Tooling API
Change Your Session Timeout Preference
Report Drastic Issues to Customer Support
Useful References
PDF

Kill a Debugging Session in Setup

From the Apex Debugger page in Setup, you can easily kill any debugging session in your org—even sessions belonging to your coworkers. Please use this power compassionately!
  1. From Setup, enter Apex Debugger in the Quick Find box, then click Apex Debugger.
  2. Click Kill Debugger.