**** Be SURE to save any sketches to a safe location before deleting any of your installation, or you may lose your code forever! Don't say I didn't warn you. ****
That said, if you are running from an Arduino IDE straight out of a zip download file, then you should delete two folders. One to clear out the executables and one to clear out any libraries.
- delete the folder the Arduino.exe is located in
- delete the folder containing your sketches and any libraries you've downloaded
The second folder can be found by opening the IDE and looking in File/Preferences for the folder named below the text that says "more preferences can be directly edited in the file". In my case that would be the folder named "C:\Users<username>\AppData\Local\Arduino15" where the preferences.txt file resides. Your location may be different, so check under File/Preferences in the IDE to be sure.
Best of luck!