For WP Masonry Lite Version

1. Download the plugin zip file from here
2. Upload the plugin files from Plugin > Add New > Upload from WordPress Admin Panel
3. Activate It
4. You can also search Wp Masony Layout from Plugin > Add New > Search and install it directly from WordPress Repository.

For WP Masonry Pro Version

1. Download the plugin zip file from here
2. Upload the plugin files from Plugin > Add New > Upload from WordPress Admin Panel
3. Activate It
4. Please make sure to deactivate and delete the lite version before using Pro Version.

Reference : If you are new to wordpress plugin installation, please refer to this detailed documentation.