The usual, automatic way;

1. Open WordPress admin, go to Plugins and click Add New
2. Enter “increase maximum upload” in search and hit Enter
3. The plugin will show up as the first on the list, click “Install Now”
4. Activate & open the plugin’s settings page located in the main admin menu

Or if needed, install manually;

1. Download the plugin.
2. Unzip it and upload to /wp-content/plugins/
3. Open WordPress admin – Plugins and click “Activate” next to the plugin
4. Activate & open plugin’s settings from Media>Increae Upload Size