First you need to open your command line, and use " npm install -g npm@latest " you'll get the error like this

C:\Users\yourname>npm install -g npm@latest
npm WARN npm npm does not support Node.js v14.7.0
npm WARN npm You should probably upgrade to a newer version of node as we
npm WARN npm can't make any promises that npm will work with this version.
npm WARN npm Supported releases of Node.js are the latest release of 4, 6, 7, 8, 9.
npm WARN npm You can find the latest version at
npm ERR! cb.apply is not a function npm ERR! A complete log of this
run can be found in: npm ERR! 
C:\Users\yourname\AppData\Roaming\npm-cache\_logs\2020-08 10T09_36_56_388Z-debug.log

Go to the path where you can find the debug log( this file is found in your npm-cache folder) C:\Users\yourname\AppData\Roaming

Delete the NPM and NPM-Cache folder, but DO NOT reinstall node . once deleted go back to your command line and re-use the command " npm install -g npm@latest "

Thanks to this author: