If not already installed, install the .NET 4 framework

Unzip KerbalEdit to the location of your choice and run KerbalEdit.exe Microsoft .NET 4.0 Download Page

Quick Reference

1. Open a KSP Install by Typing in the path of your KSP install and clicking "Load" or clicking "Folder" and using the picker.
2. Navigate your files and data using the tree. Don't worry! Nothing is changed unless you make an edit and Save it.
3. Edit data values directly just as if you were editing the file, get to your data elements quicker.
4. Data Values and the tree items that hold them highlight to let you know what has been changed since the data was opened
5. Right-Click menu on many nodes provide quick access to a number of quick update method

For additional support: KerbalEdit CodePlex Home