To run your Next.js application on a different port (other than the default port 3000), you can specify the port directly when you run the development server using the `dev` script in your `package.json`. Here’s how to do it:

### Change the Command in the CLI

You can specify the port directly in the command line when starting your Next.js application. For example, if you want to run it on port 4000, you can use:

```bash
PORT=4000 npm run dev
```

### Modify `package.json` (Optional)

If you want to make this change permanent for your development environment, you can modify the `dev` script in your `package.json` as follows:

```json
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1",
"dev": "PORT=4000 next",
"build": "next build",
"start": "next start"
}
```

### For Windows Users

If you are on Windows, the `PORT=4000` syntax may not work directly in Command Prompt. Instead, you can use the `cross-env` package for cross-platform compatibility. First, you need to install it:

```bash
npm install --save-dev cross-env
```

Then modify your `package.json`:

```json
"scripts": {
"test": "echo \"Error: no test specified\" && exit 1",
"dev": "cross-env PORT=4000 next",
"build": "next build",
"start": "next start"
}
```

### Verifying the Change

Now, if you run `npm run dev`, your Next.js application will start on port 4000 (or whichever port you specified), and you can access it by navigating to `http://localhost:4000` in your browser.

### Conclusion

To summarize, you can temporarily change the port using the CLI or make a permanent change in your `package.json` file by modifying the `dev` script. If you need cross-platform support, use `cross-env`.