When trying to clear my eeprom on 1.8.2, with an Genuine Uno for CNC I get the following message. "Arduino: 1.8.2 (Windows 7), Board: "Arduino/Genuino Uno"

Sketch uses 764 bytes (2%) of program storage space. Maximum is 32256 bytes.
Global variables use 9 bytes (0%) of dynamic memory, leaving 2039 bytes for local variables. Maximum is 2048 bytes.
avrdude: ser_open(): can't open device "\.\COM5": The system cannot find the file specified.

Problem uploading to board. See for suggestions.

This report would have more information with
"Show verbose output during compilation"
option enabled in File -> Preferences.

Were do I go from here. I know so little about this I'm less than a novice. Thanks for any help I get.

The problem has nothing to do with the eeprom_clear sketch. This will happen with any sketch because it's an upload problem. You need to select the COM port of your Arduino from the Tools > Port menu. If that menu is disabled or the COM port of your Arduino is not listed then you might need to install a driver or you may be using a charge-only or defective USB cable.