Can't upload sketch

I just bought a new arduino Nano and I am new to arduinos. I was able to upload a few sketches before but now it doesnt upload anymore.

I am getting the following error message :


Arduino: 1.8.7 (Windows 7), Board: “Arduino Nano, ATmega328P (Old Bootloader)”

Sketch uses 1688 bytes (5%) of program storage space. Maximum is 30720 bytes.
Global variables use 57 bytes (2%) of dynamic memory, leaving 1991 bytes for local variables. Maximum is 2048 bytes.
C:\Program Files\Arduino\hardware\tools\avr/bin/avrdude -CC:\Program Files\Arduino\hardware\tools\avr/etc/avrdude.conf -v -patmega328p -carduino -PCOM4 -b57600 -D -Uflash:w:C:\Users\User\AppData\Local\Temp\arduino_build_961145/Blink.ino.hex:i

avrdude: Version 6.3-20171130
Copyright (c) 2000-2005 Brian Dean,
Copyright (c) 2007-2014 Joerg Wunsch

System wide configuration file is “C:\Program Files\Arduino\hardware\tools\avr/etc/avrdude.conf”

Using Port : COM4
Using Programmer : arduino
An error occurred while uploading the sketch
Overriding Baud Rate : 57600
avrdude: ser_open(): can’t open device “\.\COM4”: The system cannot find the file specified.

avrdude done. Thank you.

This report would have more information with
“Show verbose output during compilation”
option enabled in File → Preferences.

Pls help. Thnx!

Select the port of your Nano from the Tools > Port menu.