can't upload sketch

Hi when I try to upload my sketch it says the following. can anyone point me in the right direction?

Arduino: 1.8.4 (Mac OS X), Board: "Arduino Nano, ATmega328P"

Sketch uses 6858 bytes (22%) of program storage space. Maximum is 30720 bytes.
Global variables use 280 bytes (13%) of dynamic memory, leaving 1768 bytes for local variables. Maximum is 2048 bytes.
avrdude: ser_open(): can't open device "/dev/cu.wchusbserial1420": No such file or directory
Problem uploading to board. See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.

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

Thanks Tony

Select the correct port from Tools -> Port menu.

You have selected a port that does not exist (possibly it's plugged into a different USB port and got a different number?)

Thanks your right, I uploaded a sketch yesterday and thought it would be the same for this sketch

Thanks again Tony