WordPress.org

For an automatic installation through WordPress:

1. Go to the 'Add New' plugins screen in your WordPress network admin area
2. Search for 'Hide Welcome Panel for Multisite'
3. Click 'Install Now' and network activate the plugin

For a manual installation via FTP:

1. Upload the hide-welcome-panel-for-multisite directory to the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' screen in your WordPress network admin area

To upload the plugin through WordPress, instead of FTP:

1. Upload the downloaded zip file on the 'Add New' plugins screen (see the 'Upload' tab) in your WordPress network admin area and network activate.