How to revert Gulp to original settings?

Question

gulp.js

Hello! Started learning gulp, git. I installed gulp locally, there were no errors, I configured the gulpfile.js, package.json, bower.json file according to instructions from the Internet. At the end it was written, run the gulp line, to which the command was not found in response. I went to look for an answer on the Internet, it was written to install gulp globally npm i gulp -g, which again got an error. Then I found the line command npm config set prefix /usr/local. After this command, everything flew and errors are shown.
This error after trying to install globally:
$ npm i gulp -g
npm WARN deprecated [email protected]: gulp-util is deprecated - replace it, following the guidelines at https://medium.com/gulpjs/gulp-util -ca3b1f9f9ac5
npm WARN deprecated [email protected]: please upgrade to graceful-fs 4 for compatibility with current and future versions of Node.js
npm WARN deprecated [email protected]: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated [email protected]: Please update to minimatch 3.0.2 or higher to avoid a RegExp DoS issue
npm WARN deprecated [email protected]: please upgrade to graceful-fs 4 for compatibility with current and future versions of Node.js
npm ERR! path C:\Program Files\Git\usr\local\node_modules
npm ERR! code EPERM
npm ERR! errno -4048
npm ERR! syscall mkdir
npm ERR! Error: EPERM: operation not permitted, mkdir 'C:\Program Files\Git\usr\local\node_modules'
npm ERR! { Error: EPERM: operation not permitted, mkdir 'C:\Program Files\Git\usr\local\node_modules'
npm ERR! cause:
npm ERR! { Error: EPERM: operation not permitted, mkdir 'C:\Program Files\Git\usr\local\node_modules'
npm ERR! errno: -4048,
npm ERR! code: 'EPERM',
npm ERR! syscall: 'mkdir',
npm ERR! path: 'C:\\Program Files\\Git\\usr\\local\\node_modules' },
npm ERR! stack: 'Error: EPERM: operation not permitted, mkdir \'C:\\Program Files\\Git\\usr\\local\\node_modules\'',
npm ERR! errno: -4048,
npm ERR! code: 'EPERM',
npm ERR! syscall: 'mkdir',
npm ERR! path: 'C:
\\Program Files\\Git\\usr\\local\\node_modules', npm ERR! parent: 'gulp' }
npm ERR!
npm ERR! The operation was rejected by your operating system.
npm ERR! It's possible that the file was already in use (by a text editor or antivirus),
npm ERR! or that you lack permissions to access it.
npm ERR!
npm ERR! If you believe this might be a permissions issue, please double-check the
npm ERR! permissions of the file and its containing directories, or try running
npm ERR! the command again as root/Administrator (though this is not recommended).
npm ERR! A complete log of this run can be found in:
npm ERR! C:\Users\Admin\AppData\Roaming\npm-cache\_logs\2018-09-24T11_39_55_531Z-debug.log
Please help!